Idiocracy/WMG

America is an isolated dystopia
It wasn't simply the fact that the uneducated were having more children, it was also the fact that all the smart people fled the country while the technology was still available. They were quickly becoming a minority and became sick of it. The majority of the world is now either a utopia or what it's like now. America and a few others are now viewed as "third world countries." Other countries have tried to interfere in the past with little success. There could possibly be a working time machine in another part of the world.
 * In The Marching Morons, all the supergeniuses took refuge at the south pole when they weren't busy running things for the idiots; since Idiocracy shows a much greater degree of automation, it's entirely possible.

The future is Joe's dream during the experiment. After the film ends Joe and Rita wake up a year later and completely fine.
Sure it's boring, but what kind of Army would just forget a revolutionary experiment like that so easily? It might also be something of Joe's expectation of the future laced with cynicism not associated with him personally during the film.
 * ...An army full of increasing numbers of idiots?
 * After one year? Should still be more or less the same as always.
 * It's implied only a couple of people knew about it and since the lead researcher got busted, they probably wanted to distance themselves from it.

The movie is the earth for Alpha Centauri.
Theres pollution and poverty everywhere and similar to the 1st theory, a bunch of people flew to Chiron on a spacship to start life anew.

Idiocracy is the future of Atlas Shrugged.
Galt's Gulch exists somewhere, and the Galtians are hiding out. Alternatively, they got buried the the great trash avalanche.

Idiocracy is a documentary produced by a time traveler from the future.
Surely you've heard that "Idiocracy is so true" before... but not like this!

There's more to the intelligence reduction than meets the eye...
The premise at face value is honestly offensive 19th century junk science. They suggest that the trailer trash guy is that way because he was just born a stupid yokel and it had nothing to do with substandard education or lack of opportunity or self-destructive cultural factors -- all right, they were suggesting that the cultural factors were the result of the stupidity. The "smart" couple were that much smarter not because of better education and cultural factors -- again, they would say that the intelligence caused the cultural factors. It was all a matter of genes, and this is generalizable to society in general ... and it is hard to swallow.

But what if there was more to it than that?

In Peter Watts's Rifters Trilogy, there is a mention of biotech corporations deliberately spreading buggy genotypes to create more sick people, who then require expensive treatments and become potential customers. Perhaps Idiocracy is the end result of something like that.

Say that somebody released a virus that would infect people, attack the sperm and egg, and change the genes that influenced intelligence to make the victim's children subnormal. The victim would then have to seek an expensive medical treatment for their children. Most people couldn't afford it, but the virus's makers figured that was OK because they would still make a profit from the people who could afford it and because they're evil bastards. Of course, they would want to make sure that the virus wouldn't be obvious, since they don't want anybody to realize what they did. Thus, they designed it to change a different randomly selected collection of genes in each victim or each target cell (this assumes that there are many genes that influence intelligence, but that's plausible). If many of the altered genes were dominant, then the first generations born after the virus would be only lightly effected because they would have only a couple of buggy genes; in many cases, the damage wouldn't even be noticed.

But, as the different affected lineages interbred with each other, the offspring would accumulate more and more buggy genes with each generation; thus, with each generation, people would get stupider. The virus would spread better among populations where general health was poor, access to medical care was restricted, and (assuming the virus is transmitted by bodily fluids) condoms were inadequately used, which would mean that the effects would show up most dramatically among the poor and uneducated.

Once you started to get significant portions of the population that were dramatically affected, then "stupid people breed faster" might kick in and enhance the effect.

The virus was subtle enough that nobody ever found out about it. Since no one knew what caused the decline in intelligence, the stupid people breeding faster seemed a plausible scapegoat.

It doesn't necessarily have to be Corrupt Corporate Executives who did it. It could be some crazy cult with access to genetic engineering technology, or an alien plot to weaken humanity until we're easily conquered, or a group that wanted the Idiocracy scenario to happen....

This would explain why no other nations have "stayed smart" and conquered the US. That didn't happen because the virus spread everywhere.

Joe is responsible for a holocaust that occurred after the end credits
At the end of the movie, Joe serves a short term as Vice President, then is elected President at the end of the Camacho Administration. Joe and Rita marry and have the world's three-smartest children. Frito Pendejo marries eight wives and fathers thirty-two of the world's stupidest children. After this happened, Joe realized that he had to take drastic measures to increase the median IQ of the world population.... As drastic as killing as many stupid people as possible, or castrating them before they can reproduce.
 * This actually happens in the short story The Marching Morons.

Idiocracy is the prequel to WALL-E
This is obvious. Shortly after Joe was elected President, he came to realize that humanity couldn't survive in the long term on a trash-covered world. During his administration he got Brawndo, Costco, and Carl's Jr. to merge into "Buy 'N Large" in hope that one huge corporation could be better managed. Once humanity launches into space, he hopes that we will survive long enough to return. A few centuries later, we get the events of WALL-E.

Idiocracy is the future of the Schneider verse.
Cross-posted from the iCarly WMG page.

Rupert Murdoch is still alive when the film happens
And he is keeping FoxCorp. on track, whatever track that is.

Think about it: in this future, Starbucks is essentially prostitution, and Costco is a whole city. Yet Fox News still shows news. The anchors do it naked, but they still show the news.

Think about MTV (a Viacom company) from today. Fox News from Idiocracy shows less Network Decay than our MTV has despite its being around for much longer. The anchors being naked can be attributed to their pandering to the Lowest Common Denominator, something FOX and its related media outlets are already doing, albeit in other ways.

Thus, we can assume that all the remaining smart people are working for news agencies feeding the population whatever information they deem necessary.

Questions to ponder: does The New York Post still exist, and what is it printing? Is Bill O'Reilly still around doing his political talkshow stuff?

Eventually, Joe and Rita's bloodline will be well protected viewed as monarchs
If their children are nearly as intelligent as them, and this trend continues, then everyone else will realize that they need their bloodline to survive. This will lead to the office of President not being electoral (assuming the president was still elected) and Joe and Rita's bloodline consistently ruling, until the bloodline dies out, the descendants stupefy, or people become intelligent enough to run their own lives again.
 * Unfortunately, those three children are the part of the only intelligent family. Having grown up in a home environment of intelligent people, they are most attracted to intelligent people. Either their dynasty will have genetic defects due to inbreeding, or the parents will have a tradition of taking away infants, raising them intelligently for the purpose of providing their children with intelligent spouses.

Not everyone became stupid, the smart people just left
In general, intelligent people consider intelligence attractive, and are as or more fertile than unintelligent people (the into sequence explains why people with impotence and/or heart problems don't reproduce, it had nothing to do with intelligence). Therefore the intelligent people bred with each other and became more intelligent, while the unintelligent people derided them as "geeks" and stayed away. Over time, humanity separated into two distinct species, one of which is portrayed in this film, and the other of which saw what the morons were doing to the planet, developed space travel, and left. The history you are given during the film is the story they told to cover their escape.

There are still smart people left.
And they're all Corrupt Corporate Executives running everything behind the scenes. Who else do you think makes and maintains the automated machines, infrastructure, television shows, Ass Master, etc?

Going alternatively from the theory above me, the smart people keeping themselves smart made the Too Dumb to Live populace easy to manipulate, and they eventually became the ruling class. (President Comanche was presumably just a puppet.) The way they stay in power is by Bread and Circuses and the bare minimum of stable infrastructure to keep the people complacent and not rioting. And of course, plugging your product into every possible application, suited or not, for the sake of maximising profit.

Idiocracy takes place in the future of the Office Space world
With the Secretary of State being Michael Bolton's descendant. It makes sense given Bolton's preference for gangsta rap and that they're both played by the same actor (David Herman). Though Bolton was smart, he could have had an offspring that wasn't nearly as smart as him, and that offspring ended up producing a line that survived till 2505.

Idiocracy is actually part of a large-scale social experiment
To provoke idiots, classists, and assorted bigots into demonstrating their firmly-held illusions of superiority. Given how many people seem to take the film as completely accurate/prophetic, the experiment worked. Disturbingly well.

Idiocracy takes place in Nineteen Eighty-Four, only in a Prole sector in America.
The reason why the smarter people don't exist is because they were liquidated (or the few smartest ones became the Inner Party) while their descendants are subjected to constant surveillance and finally corrupted with Newspeak. They're the ones maintaining the Bread and Circuses machinery, in fact. Alternatively, the reason why the Thought Police did not liquidate Joe is because the Party succumbed to its Newspeaking and Doublethinking so much that it essentially completely ignored the Proles.

Idiocracy takes place in the same universe as The Time Machine.
Basically, building on the idea that there are still smart people around underground, building and maintaining the technology underground, they will eventually evolve into two separate species. The idiots become the Eloi, while the smart people become Morlocks. All the problems shown in the film is simply the bugs in the system that will eventually be worked out.

The issue is not actually the lack of intelligence.
It's a lack of caring. Using the comparison between the stupid guy and the smart couple from the beginning, the smart couple is overly cautious, not wanting to bring their future child into a world they see as not being ideal. Conversely, the stupid guy just doesn't give a shit, spreading his DNA wherever he cares to. This causes a spread of people who are raised to be passive and to expect things to be handed to them, as conscientious people die out or give up, resulting in a world where people just don't give a shit that they are on the brink of starvation and/or being suffocated by their own garbage

"Idiocracy" is an actual ideology in the future.
While genetics can play a role in the individual brain's processing power, what one does with that brain tends to determine how intelligent one is; even people with terrible deficiencies can have social talent, or be good at mechanics, or come up with a creative idea once in a while. What really dragged down everybody's intellect in the future portrayed in this movie is that stupidity came to be genuinely popular as a kind of romanticized revolt against the overuse of "stupid" and all of its synonyms to describe one's political opponents. Instead of being ashamed of alleged stupidity, some political candidate proudly proclaimed his ignorance of all the things the arrogant "faggy" intellectual class "knew" that just weren't so, and was swept into power in a landslide by young voters convinced that being an "idiot" in the eyes of the decadent "fags" from the previous generation was cool. (They also regularly started calling these intellectuals "fags" in order to shock and offend their politically correct parents.)

From that time on, stupidity became the new cool, and every following generation took the idea and ran with it even further, possibly reaping further benefits from stupidity by blending it with other political agendas such as pacifism and debt reduction. ("Vote for me: I'm so stupid, I don't even know how to start a war!" "Vote for me: I'm so stupid that when it's time to mail the welfare checks, I don't know where to send them!") Uhhhmerica (the nation's actual official name) is now a one-party state run by the Idiocrats, with the primaries being the actual election and the supposed general election really being the Idiocrat's candidate pretending to be running against the Stupublican candidate from Canduhhh. Every year, each side proclaims victory over the other in their respective countries to much general rejoicing, and everyone's belief that ignorance is bliss is reaffirmed for another four years.