Among the many, many complaints regarding last night’s season finale of Dexter—and the season as a whole—none have been so vehement as those regarding the sudden revelation that [SPOILER] Deb has finally fucking realized that she is in fucking love with her fucking brother, fuck fuckity fuck fuck. Indeed, many have complained that the motivation behind Deb’s feelings and her subsequent rush to yell-cry them at Dexter lack the clear, organic progression and integrity of character that has been the hallmark of the show’s later seasons, or that its last-minute introduction is nothing but a tacked-on contrivance that feels both unearned and like a completely unnecessary twist to the finale’s even bigger, more logical reveal.
But hey, maybe you just have a problem with love? That’s the theory that showrunner Scott Buck has been floating today in his post-finale interviews, part of a general clean-up that includes addressing lingering questions like what’s up with the weird computer guy and the hand (“At this point, we have no idea what kind of message he’s sending”) and the so-called “dummy needle” (“It was not a dummy needle... We showed him emptying the needle seconds beforehand, but it didn’t look right [in post-production]”). So to answer your question: They don’t know either, and what looked like a huge plothole was just an aesthetic decision. Sometimes you have to just wing these sorts of things when you have 12 whole episodes to crank out every year.
But as for the big stuff, well, Buck tells both The Wrap and Entertainment Weekly that the Dexter/Deb romantic twist has actually been talked about in the writers’ room since around the second season, and that “It just felt like those kind of feelings were very integral to the character of Deborah, that she was in love with her brother without even realizing it.” He also claims, “We did some research on that among adopted siblings. It does exist and it does happen, and it does create a very awkward situation.” So there.
So really, he can’t believe anyone would have a problem with creating that kind of situation in their own characters, unless they just can’t handle love or something: “I find it kind of interesting that people are uneasy about Deb’s love toward her brother. That on a show about serial killers, it’s the idea of love that makes people more uncomfortable.” And really now, have we all grown so cynical that we can’t allow the increasingly outlandish plot contrivances that shape some of television’s most sloppily realized ciphers to lead them to incestuous love, just because that will make it easier somehow to delay Dexter’s fate for two more seasons? Did your mom not love you enough to create an awkward situation or something?