Loughner also bought his pistol from Sportsman's Warehouse, and Cho legally purchased both of the guns he used. All three of these people, by the way, had recorded histories of mental illnesses. I'm sure the statistics get skewed more when you're talking about high school shootings, but of course kids aren't buying their own guns.
And even if you are right, all it means is that you should do mental health screenings as a part of a firearms licensing program, and create legal penalties for making firearms available to people who don't have such licenses (or storing them unsafely).
No, it's not. The NRA's argument against gun control and mental health screening is that it's not a complete solution, so therefore it's totally ineffective and nothing should be done! I'm not pretending that it is a complete solution, but I am saying that these measures will reduce gun violence perpetrated by the mentally ill. Standing up and screeching that "WELL IF IT WON'T COMPLETELY SOLVE THE PROBLEM THEN WE SHOULD DO NOTHING" is just moronic.
If I were cherry picking I would be ignoring the Toronto mall shooting from earlier this year. That was organized crime, and obviously Canada's gun control laws couldn't have prevented it.
On the other hand, Cho, Loughner, and Holmes all had recorded histories of mental illness. So the real question is, how many times are you going to tolerate these kinds of shootings before you figure out that doing nothing isn't going to solve the problem?