In Australia, there are no "jail-style" security in univeristies and there has been few (if any) gun-related violence in schoolyard/university campuses. Why? Because guns are illegal here if you aren't licenced to own one.
People say guns don't kill people, people do. However, only a very small percentage people in society have access to black markets. I do not believe (and there has been no report in news ) of Cho having access to black markets.
By legalising civilian ownership of guns, you are giving EVERYONE easy access to weaponaries. There is no regulation of guns falling into the wrong hands. Sure, a small proportion of the society have underground association, but the overall percentage is extremely small.
The argument of everyone owning guns so that in the rare circumstances of violence, you can shoot the criminals back does not justify the hugely increased access to dangerous weapons to general public.
Anyway, if I have a choice to live in USA or Australia, you know which one I am going to choose... purely to live longer