I had a good minute to think about it this morning watching Morning Joe, and I think he hit the nail on the head.
Why do so many Americans own "assault rifles" ?
People are afraid. White people are afraid they're losing their position in this country. Look at the period between 2000-2010
2001 - 9/11 attacks
2002 - war in Afghanistan
2003 - war in Iraq
2005- - Katrina
2008 - housing bubble bursts
2009 - economic collapse
I think after all that, a lot of Americans saw the it as the decline of the America they knew. Look at American politics now. Everything is politicized and everyone is sticking with their tribe and there's no real discourse. I bought my first AR right before the 2008 election, mostly because I saw a lot of things that had me genuinely scared. I remember hearing the rhetoric of sheriffs and militia groups saying if Barrack Obama was elected it would lead to civil war, or a race war, or some other type of civil discord.
I also understand why many people there are no practical purposes for an AR, AK, or other .mil style rifle. Even if you took away the sporting purpose of the AR (i.e. it's cheap, dependable, ammo commonly available, easily customizable, accurate, light) there are still people out (especially in rural communities) there that use firearms because theres a legit need. I won't ever have to worry about feral dogs, coyotes, or wolves killing my live stock (that one depends on for food and money, i.e. survival), but for a lot of people, that's something they have to worry about. If something bad happens to me, i'll generally have a police officer at my door within a few minutes. For people that live in rural communities, a police call could take 45 minutes to an hour.
In the old days, the everyman rifle was a lever action action chambered in 30-30 with 8 rounds in the tube. Just like everything else, the everyman rifle has turned into a smaller, lighter, more effective machine that gave us the proliferation of the AR 15 as America's rifle.
I don't know if there's an answer. I heard someone say this is a problem we cannot solve, but we can manage it. I think I agree with that, with where we are now.