I'm not convinced that they should necessarily be illegal to own (or controlled, like owning a tiger is). But certainly the owners should be prosecuted for assault with a deadly weapon or negligent homicide or some shit like that.
The arguments that are made by the pro-pitbull lobby are so absurd. Like "they're really sweet dogs if you raise them right", "my dog is my companion how dare you outlaw it", blah blah - you know what? a Schnauzer is also a really sweet dog if you raise it right, and it could be your companion, and it won't bite off your baby's face. There's just absolutely no justification for why you would have that dog instead of a safer one.
This is also another one of those cases where I wish social scorn would step up. We shouldn't really need the government to intervene here. When someone says "hey wanna meet my pit bull?" you should respond with "keep that dangerous thing away from me, you deranged psychopath".