Drinking the Kool Aid

I think a good idea for a new Broadway musical would be Jonestown!, featuring the toe-tapping finale, 'Don't Drink the Kool-Aid!'

—R.M. Weiner

Stock Phrase used to indicate that someone has bought into a proposition, with the implication that they really shouldn't have.

The phrase originated with Ken Kesey's use of LSD-spiked Kool-Aid to trick people into trying drugs and convincing them to buy into drug culture. It took on new meaning and popularity upon the Jonestown massacre, where many members of a cult committed suicide or were murdered by means of poison distributed via a similar beverage called Flavor Aid, which thanks to this phrase is often misattributed to being Kool-Aid. It should also be noted that in the Jonestown incident, the victims knew the drink would kill them; some were forced at gunpoint.

This phrase, and related connotations, are commonly used on all sides of Strawman Political arguments.

Examples of Drinking the Kool Aid include:

Literature

In The Dresden Files novel Changes, Harry uses the phrase in front of the Merlin. He looks confused, until Captain Luccio says "the mass suicide in Jonestown last century," at which point he understands the term.
Sisterhood series by Fern Michaels: The entire Sisterhood and their allies have this sort of mentality. They believe that Revenge, inflicting the Fate Worse Than Death on their targets, and acting like all-around Jerk Sues are great ideas. Fortunately, Maggie Spritzer came to realize that this trope was going on, and essentially left them by the final book Home Free.

Live-Action TV

Used twice in The West Wing, both times referring to President Bartlet's senior staff.
On Lost, Sawyer uses this phrase to describe the followers of the Man in Black.
The Veronica Mars episode "Drinking the Kool Aid" sees Veronica investigating a commune/possible Cult. Her Sidekick, Wallace, eventually does an episode Title Drop.
In What Not to Wear, a fashion show thing, Stacy London says this when the Victim of the Week starts to come around in one episode.
Invoked on Community during a discussion of Pierce's beliefs. Pierce's faith believes that when Buddha returns everyone will merge into shimmering ocean of knowledge that tastes like Hawaiian fruit punch. Let's hope it doesn't come to that.
- This sounds familiar...

Video Games

In one of Gaia Online's Evolving Item Reports, a cultist offers Timmy some nice, refreshing Flavor-Aid (Timmy suddenly has to go to the bathroom very badly and doesn't have time for a drink). Gaians everywhere cried Dude, Not Funny.
In the Going Rogue expansion for City of Heroes there is Resistance graffiti stating 'Don't Drink the Cole-Aid', referring to Praetoria's emperor, Marcus Cole, and the beverage Enriche.

Web Comics

Something Happens: "Oh NO!".
In Sinfest, Monique is offered some.

Western Animation

Parodied on an episode of Family Guy. Meg unknowingly joins a cult trying to be popular, wherein the leader of said cult tries to initiate a mass suicide through... You guessed it. Stewie kills him.

Real Life

In the US Navy's Surface Warfare Officer (SWO) community, signing a contract to become a Department Head is often referred to as Drinking the Kool Aid. Department Head is the next step up after the entry job, Division Officer, and officers face the choice to re-commit for DH or resign after 4–5 years of service. It's also seen as one of the most stressful jobs in the Navy, and by signing up you're committing yourself to at least four years of it; so the implication is that if you sign on and take the bonus, you've fully bought into the "SWO Propaganda".