Sex Is Evil

In most media, there is a prevalent fear of sex. Moral Guardians and others have always disapproved of sex more than violence (the Hays Code famously outlawed anything that even remotely implied sex, whereas hangings and executions could be shown "within good taste"), for some reason.

So, of course, adding sex automatically makes works Darker and Edgier.

Want to add menace to your villain? Have him make sinister advances towards the heroine, or the hero. Want The Ingenue to make a Face Heel Turn? Get her laid.

In older works, Sex Is Evil could also be used as a free pass for the hero to be a total jerk under the banner of Sex Is Evil and I Am Horny. For example, he could sexually abuse women (including way too young ones), and then show his goodness by forgiving them for tempting him.

See "Good People Have Good Sex" for what's effectively its inversion.

Tropes that are influenced by this include:
 * Beauty Is Bad
 * Bondage Is Bad
 * Bury Your Gays
 * The Cheerleader
 * Death By Sex
 * Defiled Forever
 * Evil Is Sexy
 * Horny Devils
 * I Have You Now My Pretty
 * Nature Adores a Virgin
 * No Sex Allowed
 * Sex Is Evil and I Am Horny
 * Virgin Power

No Real Life Examples Please!

Anime and Manga

 * Full Metal Panic. Sousuke is a Chaste Hero who is obviously a virgin and doesn't understand anything about sex. And then to contrast, there are the villains from Amalgam who have a huge array of weird kinks and depraved tendencies. Gauron, a sadomasochistic, Depraved Bisexual pedophile and necrophiliac who displays most of these kinks towards Sousuke. Gates, Ax Crazy Lolicon rapist who masturbates to animal nature videos (and is very likely a necrophiliac as well, though not as explicitly stated). And the Twincesty Creepy Twins Xia Yu Fan and Xia Yu Lan, who most likely had something going on with Gauron and are shown to be rather promiscuous (with them seducing the AS repairmen in Amalgam). Even the villainous female scientist who only had a small part in the beginning has depraved kinks. In the novels, she's shown to enjoy Gauron strangling her as much as he does. He even lampshades it by mocking her with amusement. To go further, even Leonard is not exempt from this - in the novels, when he's first mentioned, he's shown to be a rather loose playboy that sleeps around. Over the phone, he's heard to have had sex with a woman with a high nasal voice.
 * Neon Genesis Evangelion, with its focus on adolescence and pathology, broadly hints at this trope more than once. In particular, the Mind Screw collage in End of Evangelion includes a shot of Shinji screaming while the word "SEX" flashes across his face.
 * It's difficult to tell whether Speed Grapher is anti-sex or just anti-fetish, but it's definitely anti-something. How healthy a relationship is tends to be inversely proportional to how sexual it is, and all but one sexual fetish in the series either requires killing or mutilating people, or leads to killing or mutilating people (sometimes for no apparent reason, as when the tattoo fetishist kills the girl he's dating.)
 * Damn near every sex-related scene in Berserk, consensual or not, is used to gross the hell out of the audience. Never mind all of the rape that goes on (and how the product of said rape can produce evil itself), but you have Slan, who is a Gorgeous Gorgon with BDSM tendencies and leanings, you have Wyald, who doesn't have the decency to hold off on having sex with dozens of women in the middle of a conversation, then you have the pagan worshipers and their disgusting psychedelic orgies, and the numerous, NUMEROUS phallic and vaginal imagery in various monster designs...
 * Not to mention that sex was linked to  downfall when he has   The scene was not particularly romantic...

Comics

 * Rorschach is a firm believer in this trope. Of course, he is crazy, and his mom was a prostitute of the most Crapsack World kind, so it's not hard to see why he has the idea.

Film

 * Played straight in The Wicker Man (the original, not the newer version), in that the straight-laced Christian officer is shocked at the depraved sex and immorality surrounding him on the island, believing that they were evil heathens
 * In some cruel irony,.
 * Zardoz: THE PENIS IS EVIL!!!

Literature
""Whatever quality of human greatness I have the talent to portray--that was the quality the outer world sought to degrade. They let me play nothing but symbols of depravity, nothing but harlots, dissipation-chasers and home-wreckers, always to be beaten at the end by the little girl next door, personifying the virtue of mediocrity.""
 * In Dracula, being bitten is interpreted as a metaphor for sex (although Van Helsing himself actually laughs at seeing donating blood as a metaphor for sex). When Dracula bites the unconscious Lucy and forces Mina to drink his blood (both against their will), it's evil. When Lucy's fiancé, 2 admirers, and Van Helsing give her blood, it's redemptive. Jonathan and Mina are married and sleeping together, which is not portrayed as evil any more than Lucy's excitement at becoming engaged to Arthur. In this context, rape is evil, but mutual, passionate love is portrayed as necessary, healthy, and beautiful, which is quite an impressive distinction for a Victorian novel to make.
 * It might surprise some people, but this trope is averted in The Bible. Sex is to be used within marriage, and there are whole chapters devoted to it, e.g., not going with "strange women" (harlots), with reasons given, but there's also a whole book (The Song of Songs aka The Song of Solomon) devoted to sex and romance ("her breasts shall satisfy thee always"), and there's even bits in the New Testament about not "depriving" your mate of sex, except by mutual agreement for a short time.
 * Also, the very first command God gives to Adam and Eve is, "Be fruitful and multiply," and his first command to Noah, after the The Great Flood, is, "Be fruitful and increase in number and fill the earth."
 * The Party preaches that sex is like a minor and disgusting operation, all as part of an attempt to corrupt the sex drive.
 * Keira in "Scourge the Heretic" is a psychotic zealot assassin raised in a Sex Is Evil Redemptionist society that believes killing sinners is righteous and everyone has done something. Unfortunately for her faith, she is also a teenage girl. Hilarity Ensues.
 * Some people have interpreted C.S. Lewis' The Chronicles of Narnia this way; specifically a bit in 'The Last Battle'. Here, all the Earth-humans who ever came to Narnia gather to help it one last time- except Susan. She apparently became interested in lipstick and boys, and was no longer pure enough to believe in Narnia. This gives the Unfortunate Implication that a sex drive means you can't enter Heaven.
 * In Atlas Shrugged, former movie actress Kay Ludlow complains about this trope applying to her roles:

""Get that filth out of here!""
 * Asher in Someone Elses War doesn't even want to see it suggested that people are having sex.

Live Action TV

 * One of the more frequent knocks on CSI is that this is pretty much how any sex practices outside of the norm come off.
 * One significant exception is Lady Heather, a dominatrix who is consistently portrayed as a mentally balanced and sympathetic character. She even develops a friendship and possibly has a brief romantic relationship with Grissom., but this is not really related to her sexuality.
 * This would seem to be the 'moral' being raised in American Gothic, unsurprising for a show where the Big Bad is essentially Satan, known for using lust as his primary weapon. Not only does Selena spread her legs at the drop of a hat for Buck (or to corrupt Ben, or Dr. Peele, or...), but Buck himself seduces Gail into a cringing Distressed Damsel, it was his rape of Mrs. Temple that started everything, and even Merlyn's desire for a normal life (complete with a love interest) almost costs an innocent baby its life and leads her to suicide and a return as an avenging angel. Oh, and when Buck corrupts the wife of a hospital orderly with a magic mirror, what's the first thing she does? Turn on the seductive charm.
 * Joss Whedon did this so much in the early seasons of Buffy the Vampire Slayer, in the fourth season he made an episode that was all about subverting it: "Where the Wild Things Are" was dedicated to exploring a haunted house that punished people for sexual activity.
 * What's weird is that he expressly says in interviews and the DVD commentaries that he created the character Buffy to subvert this (well, the trope of the blonde girl always being killed off in horror films, but he considers the death = punishment for having sex is a part of that trope).
 * Angel frequently had this trope, to the point in one episode in the first season Cordelia was searching for a lesson to learn from the experience and eventually settled on "sex is bad", one which Angel immediately agreed with.
 * Seventh Heaven
 * Margaret Cho fell victim to this trope while filming her sitcom All American Girl. The series was based on her life, and Cho wrote in her autobiography how the producers would make her character refuse any and all sexual advances, even situations where she herself would have consented.
 * House had a lot of episodes, especially in the first two seasons where the Disease of the Week was tied in some way to sex, often outside of marriage (affair, unmarried couple, etc), or thought to be at some point in the episode. This culminated in a second season episode called, naturally enough, Sex Kills.
 * This seemed to be part of the general theme of Robin Hood. There are only two people that definitely had sex on the show: Guy of Gisborne with a serving maid, and one half of an Abel and Cain pair of brothers (naturally, the evil one). But apart from that, both Robin and Marian were portrayed as being sexually attracted to the Gisborne siblings: Guy and Isabella. They are both punished severely for their "lust".
 * Marian is eventually murdered by Guy in death scene that is deliberately filled with sexual symbolism, and which creator Dominic Mingella calls "the consummation of Guy and Marian." After Marian's death, Robin finds himself in a Love Triangle with Isabella and Kate, who embody the Madonna/Whore stereotype. Isabella sucks on strawberries, carries money in her garter, wears seductive red dresses, and has escaped an abusive marriage. Kate is a peasant virgin with a crush on Robin who instinctively distrusts Isabella. Naturally, Isabella turns out to be evil, revealed after she tries and fails to lure Robin away from his calling as a hero to the people. She eventually murders him. Lesson: if you're sexually attracted to someone, they will kill you.
 * Vaal forbade love and sex to his primitive subjects in "The Apple" episode on T.O.S..

Tabletop Games

 * In Warhammer 40000, sexual activity of any sort feeds the Chaos god Slaanesh, (though excess of anything will as well) which is the Cosmic Horror manifestation of desire, lust, and similar emotions. Eldar have to be very cautious during reproduction, or Slaanesh is liable to rip their souls from their bodies...

Video Games

 * Baldurs Gate II allows you to romance party members. Sex with them has an even split on negative consequences. The final dialogue for Jaheira's takes place between you and her the morning after, and the only one where coupling appears before the end of the relationship at all is with Viconia, an evil character. Meanwhile, if you sleep with Aerie, it breaks the romance. The expansion allows (literally) Good People To Have Good Sex, plus you can convert Viconia from The Dark Side and impregnate Aerie.

Webcomics

 * Surprisingly, this seems to be the moral of Sexy Losers, though it's a bit more complex than most instances of this trope. The characters who engage in sex aren't (usually) evil at heart, but as they become obsessed with getting more and more sex, they become less and less interested in who they're having sex with, treating others only as tools (or more accurately, blow-up dolls.) In one case, it's been openly stated that a character will die alone and unloved unless he can learn how to actually love people and not just lust after them.

Web Original

 * This meets Fetish Fuel in some stories on The Erotic Mind Control Story Archive, with a rather populous sub-genre of stories where the sexual act is the method of a corrupting, controlling force. Also found if you poke around its host/ sister site asstr.org (NSFW) in the stories of Stephen Gray and others. The application of the trope in the stories ranges from cheesy bordering on Parody (intentional or not) to downright Nightmare Fuel-- which may be just your thing.

Western Animation

 * The South Park episode "Good Times with Weapons" left Butters with a shuriken stuck in his eye, but none of the adults (except arguably Butters' parents) cared they were more concerned with Cartman's naked walk across the stage at an auction that most of the town was watching. Stan hit the nail on the head: "Parents don't give a crap about violence when there's sex stuff to worry about."
 * "If you have sex, you're automatically in Al Quaeda."