The most shocking revelation in Sunday's season finale of "Dexter" (spoiler alert!) came when Deb Morgan admitted that she harbored romantic feelings for her adopted brother, Dexter.

Randy Tepper/Showtime

exter's controversial season finale Sunday night was a stunner. (Warning: Spoilers lie ahead.) And the night's biggest jaw-dropper didn't come when, after six seasons, vigilante serial killer Dexter Morgan's murderous double life was finally discovered by his sister, Deb. Instead, it was Deb's squirm-inducing revelation that she harbors romantic feelings for Dexter, her adopted brother. That makes Dexter the fourth cable series to unveil a divisive incest storyline this year, following HBO's trio of Bored to Death, Game of Thrones, and, most recently, Boardwalk Empire. It's a "troubling trend" that's been building for years on shows like Nip/Tuck, Lost, and the aptly named Brothers and Sisters, says Jace Lacob at The Daily Beast, but is just now reaching critical mass. For better or worse, does that mean the taboo is broken?

Of course it's a taboo. That's why it's intriguing: Incest is still very much a taboo subject, says Tracy Clark-Flory at Salon. And it's also still horrifying. Shows like Dexter and Game of Thrones aren't breaking the taboo by depicting incest, they are reinforcing it "by playing on our supreme squeamishness toward the idea." It's telling, too, that these shows are still quite popular in spite of their portrayals of incest. "We are at once drawn to it and repulsed by it."
"Why is incest all over prime time?"

Incest may be the ideal cable TV storyline: Of course the most boundary-pushing shows on the most progressive cable networks, like HBO and Showtime, would tackle incest, says Jaime Weinman at Maclean's. "It's a taboo subject, and taboo subjects" are what producers on those networks are "always on the lookout for." These cable shows are free from the constraints of advertisers, who would ordinarily pull their ad dollars from networks that portray such topics. "Plus, as the bar gets raised for sociopathic or problematic behavior on TV, an incest story is one of the few things remaining that can be instantly shocking."
"Incest plots replace hoarder plots"

But on Dexter, it doesn't work at all: Taboo or not, the incest storyline on Dexter fails, says Jamie Peck at Crushable. The relationship between adopted siblings Dexter and Deb Morgan was "the single most important relationship on the show," and the reveal that Deb has sexual feelings for him threatens to "totally ruin that bond for fans who've become invested in it." Plus, the incest plot comes "completely out of left field." It comes off as random, disrespects the characters, and takes away from the moment that "the series had been building up to since it began."
"What's with all the incest on television this season?"