You'll always hear the argument that legalised weapons have nothing to do with gun violence. And you'll always hear the argument that if a gun were not used another weapon would have been, so gun laws will not stop violence. I will never understand either argument. To me, it's like saying 'global warming' is not man-made so we shouldn't reduce carbon emissions into the air.
Even if tighter gun laws - or an outright ban on guns - does not stop gun crime, it's obvious to those looking that gun violence such as the one discussed here would be reduced. However, there are those who will stick to their guns, pun intended, and resist any control whatsoever because they still believe in the ridiculous right to bear arms.
My suggestion to you is to hone your argument against gun ownership and write a persuasive letter to your representatives. Hell, pass the letter around and get others to sign it while you're at it. It might be a waste of time or it might help make a difference. All the discussion will do here is bring out the people from opposite ends to have the same argument as always. And then in a few months someone else will start another thread about yet one more school shooting and the argument will begin again.
"The others don't like my interviews. And frankly, I don't care much for theirs." ~ Freddie Mercury