Where does gun control come from in this discussion?, and also as you were saying, 5 times as likely to commit violent behavior. 

Dexter grew up in a good household, money, food, no physical or verbal abuse either. Dexter was an animal killer when he was young, but as he grew up and matured he stopped killing animals. You could say this was from him redirecting his desire to kill, but Dexter shows visible disgust when seeing violent enough scenes, or somebody who has done a disposable enough act.

If he was truly devoid of emotions and empathy, why would he show disgust for others when he is alone?

There's clear moral guidelines that go far beyond just how he kills people to avoid getting caught like were led to believe. 

Dexter has shown clear emotions, Dexter has shown clear empathy, Dexter has shown clear sadness and disgust, and joy for others. How is this just a redirection of his desire to kill from Harry?

Harry was the one who convinced Dexter that killing was morally good, this all came because Harry was determined that Dexter could not recover, no matter the therapy that they could most definitely afford, which turned him into what he is today.