Why is the intention to kill a human the only reason to have an "assault rifle"? Why can't you just have it to have it? Why can't I just take it to the shooting range and plink at paper?
(all "assault rifle" means is that it shoots a smaller, less powerful cartridge than a regular rifle)
Why is it so evil?
Because it has a pistol grip?
Nope, that's an ergonomic reason. Your wrist hurts like hell after a day of shooting a straight stock.
Is it because it's more powerful?
Nope, shoots a smaller bullet than hunting rifles
Is it because it has a high rate of fire?
No, because semi-automatic rifles all shoot at the same rate: one trigger pull = one bullet
Is it because they can readily accept a magazine of 20, 30, 50, 100 rounds? That surely has to be for mass murder, huh?
Or for not having to reload a million times at the shooting range while you're target shooting. I can modify my pump shotgun to shoot a 30rd drum. Who decided that the acceptable number of people dead between reloading is 10, anyway?
And here's another thing to think about:
In 1776, if the colonists weren't allowed to have modern, military-grade muskets, how effective do you think the independence movement would have been? If all the households had bows and arrows and slingshots? Not very, huh?
People these days disregard the possibility of turmoil within our own borders. Yeah, we have this great untouchable nation and yada yada yada. That's what everyone in Yugoslavia thought in the 80s, then 1991 rolled around and you had genocides, ethnic cleansing, and other war crimes, aside from regular old soldier-on-soldier combat.
Should a time arise when American citizens have to defend themselves from their own State, or from a foreign invader, or hell, a looter after a major catastrophe, I would much rather that people had whatever they felt was most effective at getting the job done.
Besides, modern military assault rifles all shoot the 5.56mm NATO round, so if you had an AR-15 (oooh, evil black gun), it would be easy to find ammunition in a crisis.