The deadliest school shooting in US history was done with two handguns.
No risk control has 100% effectiveness.
But to say "we can't fix it all, so we do nothing" is never the way to accomplish anything. The smallest improvement is improvement, and if you aren't infringing upon constitutional rights, you have to try. Because the AR ownership is a want that, apparently, they way we are trending, isn't a want the majority of the nation is willing to continue to tolerate at the level of inherent risk. It is political. People who try to jam on these kids for making the shooting "political" crack me up...yeah, they are. That is how laws get passed. The political process. They didn't ask for this pulpit. They didn't bait it to happen. This is righteous politicking.
And so much gets lost in the "school shooting" categorization of this movement. It has been driven by students (and it really is...my daughter is a local organizer and she was on a conference call with nothing but teens last night, and the organizing and funding arm for our local march was largely teen driven), and their visceral reaction at both the shootings and the threats that impact their lives through lockdowns and general terror (my daughter's school had an arrest made for a plot where guns and bomb making material were discovered) are driving their reaction.
But the laws being requested aren't just about school shootings. Waiting periods are more about domestic violence, the guy who doesn't have a gun who is pissed off and wants to end his partner's life (or her). Background checks are about making it as hard as possible for those who shouldn't have guns to have them.
It's like parenting, in some ways, but this is a democratic/representative government effort. But in using a parenting analogy, I am not talking about nanny state. I am talking about knowing your kid is likely to do some things against your rules, maybe illegal things, but making it as hard as possible for them to do so. Watching your liquor. If you are on pills that might be fun for teens, count those fuckers. Smell breath at the door after a night out. For God's sake, look in their drawers and closet occasionally...if they have a cache of guns, call someone. You make it hard for them to do something illegal, understanding they might do so anyhow.
Make it hard for the pissed off person who just got in an argument with their partner or saw them cheating to go buy a gun and execute everyone involved. If they are a felon, make them go black market. Maybe they cool off before they make it happen. Va Tech happened, but Tucson wasn't worse because the kid only had a lower capacity gun and got tackled on reload.
Of course, he went to a Walmart to buy ammo and the first one had a clerk that felt Loughner was acting "unusual" and refused him. He went to another, and with no way for the first clerk to get the word out, he bought the ammo that killed 6, including a 9 year old, wounded 13 more, including Rep. Giffords, who was no longer able to hold her position due to the damage suffered in the shooting.
When Loughner went to reload his Glock, he dropped the magazine. A bystander grabbed the clip, and someone went WWE and hit him with a folding chair. Then a 74-year old former Army Colonel, who had been shot, tackled him. If that bullet had been from a high power rifle, he wouldn't have been able to.
If his clip had been limited to 10 or 12 rather than the 33 in the Glock that he legally bought, the damage would have been, well...lessened.
Those are the situations gun control looks to mitigate. Those high profile ones, and the hundreds of "get a gun and shoot someone because I am mad" domestic violence deaths that are preventable.
You cannot eliminate them. But you cannot, if it is in the heart of the people, stop short of trying.