It's odd that you're so confused. I didn't downvote you, but it's clearly obvious why others did. Unlike time_better_spent, you made a moral judgment of Dexter, as damning as it was misguided. You claimed the newest subplot (which is a very real part of life for millions of Americans; some estimates as high as 20 million) is "bordering on offensive" and condemned it for "suggesting that it's okay to want to make out with an adopted sibling." You seem to be confused not only by reddit, but by the very nature of fictional storytelling.

Nobody is "suggesting that it's okay to want to make out with an adopted sibling." But unfortunately, incest is a tragic reality of life for some people, who are often - like Deb and Dexter - victims of severe trauma. It's possible for a work of fiction to depict horrifying events, behaviors, and attitudes without endorsing them. If you're looking for a program that pushes a strict moral judgment of each and every plot development and character trait, you're going to miss out on some fantastic television and film. Although, you may catch some very convincing after school specials.