I personally like Hody as a villain. I think Oda is a genius to create his character.
Hody has no reason to hate human, but he is unable to not hate human.
This is real world situation. A part of us is prejudiced planted by our later generation. We don't have personal experience to hate certain people which have certain attributes (asian/white/black/muslim/catholic/jew/communist, etc.), but we cannot accept them anyhow.. It seems the fishman district are a place where the fishman outcast and criminals lives, therefore hate for humans really blooms there. It is like growing up with radical parents who brainwashed me with their hate. (It is happening out there)
Is it pointless to blow yourself up to kill certain people? Yes it is! But some people has done it. I was there. Those people were desperate, they want to make a point, make a meaning of their lives. Actually they see themselves as heroes. (Freedom fighter)
Hody "hate" is his meaning in life. As long as he hate human, he will rise again and again. That's why Luffy punching /kicking him all around and a certain defeat will not make him surrender, it will just drive him to the extreme. His body is broken, but not his will.
I can't wait how Oda will resolve this conflict. How Luffy will really "defeat" Hody, cause in a real world, killing all people who hate us will not bring peace, it will only bring more hate.
There can be no real peace without justice.