Yes any dog can be vicious, it's totally missing the point though - when you have a pit bull type dog deciding to be vicious then the consequences are very different to plenty of other dogs.
Strangely enough you don't tend to see Chihuahuas on that list... fact is there are much more severe consequences if a pit bull type dog kicks off and it can lead to deaths or severe injuries. It is pretty obvious why, they're muscular little things with massive powerful jaws.
I've never encountered a gun owner I'd be worried about, every gun owner I know is very sensible, has never been in trouble with the law and would never kill anyone. I don't think that firearms should be a free for all in the UK though.
Fact is there are plenty of owners of bull terrier types who train them to be aggressive and use them as weapons (in place of knives) - go to any number of London parks and you'll frequently see low branches on trees covered in bite marks from where the owners of these dogs train them to hang from them in an attempt to strengthen their jaws, train them to be aggressive.
I'm not suggesting that current owners should need do anything more than simply muzzle their dogs when outside and make sure their neutered, IMO the introduction of Staffies to the list ought to contain some provision for current owners with just irresponsible ones who let them off the lead in the streets etc.. or who have their dog involved in attacks etc.. affected.
Fact is that owners of staffies are disproportionately irresponsible dog owners too - they're massively overrepresented in most dog kennels.