There are only two reasons for not neutering a male pit bull. Either you want him for breeding or you do not want to reduce his aggression.
Which brings me to something I found on the official pit rescue page about who shouldn't own a pit bull:
"An insecure person who wants only an aggressive dog to bolster some personal human inadequacy should never become an owner of one of these dogs. An uncaring or negligent person should not buy an AmStaff or an APBT (or any other dog for that matter)."
Yep. Ban stupid people, not dogs.