Actually, I have no interest in firing that kind of weapon thanks.
That is an excellent question. The gun itself isn't the problem, it's the availability of the gun and this person clearly had some sort of mental illness that was unaddressed. Justine Bateman hits it on the head as it were, "Why does a tragedy like 9/11 change everything about air travel, but numerous gun massacres CHANGE NOTHING?" It's going to come down to what's easiest and most cost effective to change: gun control or mental health care (since a good majority of people that perpetrate these crimes are mentally disabled in some way). There isn't a solution that will please everyone.
Oh and to go back to the "criminals will find a way" argument, why have laws at all then?
And as for your reason, you're going to carry a semi-automatic rifle everywhere you go? These shootings are happening everywhere. Malls, movie theaters, schools, churches, etc. I understand the desire to protect what's important, but that seems paranoid.