Castanet recently asked "should breeds be banned"?, to which my answer is an emphatic "no". If a dog behaves aggressively it is due to poor (if any) training on the part of the owner and/or mistreatment, not its breed per se.
Many breeds have a poor reputation due to the public's ignorance and media sensationalizing attacks by certain breeds. When I walk Loki, my Rotti/Lab cross, people complement me on how well behaved he is and many express surprise when I tell them his breed. In my experience, it is the smaller dogs who tend to be more aggressive; a bite from a small dog will draw blood just as much as one from a bigger dog.
To ban a dog because of their breed is a slippery slope we should not put ourselves on. What's next; banning certain races of people because one can point to figures that shows that they tend to be more aggressive?
Here's a parting thought: perhaps we should hold violent people to the same standards that we hold dogs. That is, if someone is found to be guilty of a violent assault, perhaps the public should demand that they be "put to sleep" in the same manner that some would insist of a violent dog.
Rich Teer