FL is one state that allows carry as well as Texas, Alaska and others.
There are a lot of violent acts all across the US. Alaska has more murders than Ontario does in a year with less than 700,000 people.
Having said that, the most violent place in the US is Chicago and they don't allow carry (open or concealed).
To me it seems that the problem exists with the US' way of dealing with background checks. The reason I believe you see much less gun violence in Canada is because of our laws regarding training and the PAL.
I would think if the US would introduce mandatory training and an acquisition type license there would be far fewer issues.
As it is you go into a gun shop and fill out the paperwork and a week later you come and pick up your gun.
Minor BG check and no firearms training needed.