Many people here have cited the dogsbite.org website. This website is flat out political propaganda. The "statistics" the site uses are very biased. Several scholarly articles and published works have discredited their numbers. For instance, they will use the number of times "pit bull attack" and similar buzz words are posted in newspapers to gather data. The same attack could be reported by hundreds of newspapers and websites and they can count every single article as an instance of attack, and this isn't the only way the data is misleading. It is flat out BS. It is very easy to skew data when you start with the conclusion, as the woman who runs this "organization" does.
Also, if these dogs were 100-120 lbs a piece rather than 50-60 lbs a piece there is NO WAY they are any of the breeds that fall within the loose "pit bull" term. 60 lbs is even large for a pit bull breed dog.
Another "fact" I have seen posted about here is that pit bulls were originally bred to kill or attack. No one linked anything for this of course because it is, again, another media rumor. Pit bull breeds were bred for multiple differing purposes, from being nanny dogs to assist with nursery care and protection, to aiding hunters of wild boars. Pit bull breeds were not developed to fight or kill humans or other dogs.
Some mainstream sources discuss dogsbite.org
https://www.huffingtonpost.com/steffen-baldwin/the-lies-damn-lies-and-st_b_8112394.html
http://www.teampitafull.org/DogsBite.html
https://www.thedodo.com/five-dog-pages-you-need-to-stop-linking-to-1091066497.html
https://www.huffingtonpost.com/douglas-anthony-cooper/merritt-clifton-pit-bulls_b_5866176.html
Scholarly articles debunking the myth of dogsbite.org
http://www.journalvetbehavior.com/article/S1558-7878(06)00012-8/fulltext
http://heinonline.org/HOL/LandingPage?handle=hein.journals/anim10&div=14&id=&page=
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1576444/pdf/canvetj00105-0032.pdf
http://www.journalvetbehavior.com/article/S1558-7878(07)00236-5/fulltext
No canine or animal organization supports banning specific breeds. The American Kennel Club, the ASPCA, the American Veterinary Medical Association, the Animal Farm Foundation, the British Veterinary Association, the National Canine Research Council, the US Dept. of Justice, the American Bar Association, the United Kennel Club, even the CDC does not support breed specific bans. These are the organizations responsible for collecting actual, scientific, objective data on things such as animal attacks. Do not let the media and it's political sways fool you.