By-and-large though we are. There are 5 million AR-10s/15s in the country (as of 2016), and a 300mil+ population.
These shootings are heinous, horrible, the worst thing imaginable. And sure, they seem to be happening awfully frequently. Thing is, they're not though, in terms of numbers of people buying them that go and commit a crime with them. Even if you take the what, 20 major incidents with these weapons over 10 years or so, that's 20 crazies out of 5 million owners that are an issue.
And those crazies would just use some other semi-automatic rifle or semi-automatic handgun or a shotgun, if you managed to get an AR-10/15 ban in place. Those other 4 000 080 owners are using them for hunting & home defence alone.
Yeah, we should make background checks tougher, find a way to raise the bar to qualify to own one of these things. You don't ban them entirely though, when the stats bear out the ridiculously tiny amount of people ever doing anything wrong with them. It's horrible what's happening, it really is. But it's crazy people, outliers, exceptions-to-the-rule, and in a big way.