Dexter is most complex villain in the series so far and I wish more people cared about that instead of making him be COMPLETELY terrible which he is not.
He did terrible things don't get me wrong, but the stuff he did (or well..tried to do) as happy fella where because he had completely lost it not because he was always like that. If I remember correctly it took him at least a year to snap. And to be fair being stuck in a doll and treated like a kid's play toy while also having uncontrollable bloodlust sounds like it sucks a lot to me. And yes even before that he hurt animals - cats even. But he did it to avoid hurting and killing PEOPLE. Compare that to villains like Bob or Moloch who have hurt and killed innocent people for no fucking reason. The fact he really tried to prevent himself from hurting people is really interesting to me not gonna lie. Even if his solution was also bad. At least he had a reason.
I can't help but sympathize with him. Although I can't tell this for sure since it's not really confirmed - I feel like he, himself wasn't really happy with his bloodlust either. I feel like in the end of the day he really just wanted to have a normal life.
I'm not trying to justify his actions - but I wish the fandom could actually look deeper to his character than just a sadistic gross cat killer. He's much more than that.