Originally posted by: Y
I think he is allowed to be a captain despite being a sick fuck because Soul Society gives leniency to him because he is the president of the research divison or whatever. His sick experiments are overlooked thanks to his contributions.

Of course, Soul Society also has fucked up draconian laws that essentially condemned Rukia to death for what amounts to traveling without a passport. And Zaraki Kenpatchi's lust for killing isn't endearing either.
He cares about his comrades. He has a lot of bloodlust, he wants to kill, but, unless they're a challenge, I don't think he's want his squad to die, he's a good captain. With the exception of not having any particular talent with his zanpakutou (aka not knowing it's name, nevermind "releasing" it), he's an awesome captain. Mayuri's just a freaky guy.