The FBI not picking up the kid after being tipped off, the sheriff's department not picking up the kid after 39 visits, or the Sheriff Deputy that did not engage the shooter, but waited for backup, all point to already existing policy that failed to be followed properly.
Even the principal himself, who evacuated a school based on an unsubstantiated fire alarm (every fire control panel tells you what switch was pulled, so he could easily have called a teacher near that station for confirmation) shares some of the blame here. Also, the fact that he evacuated multiple buildings, rather than only the building where the alarm was pulled, was a confusing mistake.
There are people who are actually trying to fix a very broken system, and they are not the ones using this to advance a political agenda.
[1] http://www.miamiherald.com/news/local/community/broward/arti...
I'd also like to point out that there are a number of issues with the current system besides what you've mentioned that could improve things. For starters, even if this person was involuntarily committed, he would fail a background check, but would still be able to purchase guns online or at a gun show without a background check. There are red flag laws, which allow people to petition the court to temporarily seize guns from someone acting in a disturbing way, which would have been ideal for this case, but these are only in some states.
Online or by-mail purchases can only be shipped to an in-state dealer, where you must complete a background check.
This has been the case for twenty years.
Neither can you do so at a gun show. The same laws apply.
You can not legally obtain a weapon from a licensed dealer without a background check. Period.
If you derive any notable income from selling weapons, then you are legally required to register as a dealer. Failure to do so is a federal felony.
This is why weapons used in crimes do not generally come from legal sources. The vast majority are either stolen, or illegally purchased by a friend of family member.
Who is doing this? Not very many, I estimate.
Even allowing your premise, they're separate issues. Gun control is about more than school shootings, and one could turn your ire back onto you for focusing only on school shootings when there are many more kinds of mass shootings out there, not to mention interpersonal fights escalating to firepower.
As somebody who personally had (and witnessed others) fights in high school parking lots with rifles in the pickup windows of the combatants (yep, I'm over 40), and never heard of anybody ever considering escalating to firepower, I have to call BS on that. I expect to be down voted, but unless you feel that people have become more evil since your father was a kid, I don't know what to tell you.
As for gang violence and other crime, I invite you to look at Mexico (or Chicago), which have strict gun control.
I'm referring to domestic violence and partner homicide.