Americans want to be able to have assault weapons because they know their freedom could be endangered by anyone on earth at any given time, wether it's their own government...or a chinese invasion and so on. Basically it's a deeply embeded warrior spirit. When you build stuff, you develop the will to defend it, at all costs. It's normal to be conservative, when you actually built, developped stuff.
You re not going to defend yourself in case of a serious conflict, with only handguns or 22 lr...
And all the people who commited these atrocious acts came from fucked up families. This is the real problem, the roots of evil, but nobody is adressing it directly.