Herein lies the problem. Not saying it's exclusive to black or white. But in this case, the people who are protesting/rioting etc. are some of the most misguided, stupid mofos on the face of the earth.
I think there are several factors at play here.
One: as you mentioned, a certain percentage of the population will always be ignorant. Hell, talk to some bama fans to understand that. Some folks are incapable of reason and self awareness. You'll never change them.
Two: We now get our media in an echo chamber. Conservatives watch fox, liberals watch CNN and they both visit rather more extreme news sites (often with even more dubious journalistic practices). They hear from literally only people who agree with their point of view most of the day. Both media bases are now pandering to the lowest common denominator type stories designed specifically to both enhance controversy and oversimplify issues (WHITE cop kills BLACK KID in a predictable outcome of violent decisions because RACISM or BLACK lunatic with serious mental illness KILLS COPS BECAUSE AL SHARPTON TOLD HIM TO in much the same way catcher in the rye told that other lunatic to kill)
Sidebar: The media now reminds me of that Pierce Brosnan James Bond villain, the one who created horrible events and then covered them for profit. They're pretty shameless about setting these fires and gleefully covering all the LCDs.
Three: Much like we see in sports fan bases, it feels good to belong to a group. And you hate to hear someone attacking your own group. As soon as you start to feel a part of one its easy to make the other guys THEM and you're an US. Whatever US happens to do is okay, because they're the good guys. Whatever THEM does is evil, because they're the bad guys. The media is using this (and other simple techniques) to set us against each other. Sadly, they're doing it for the money rather than true belief in an issue. To a certain extent you'll never totally eliminate this impulse, but it helps to be aware of this kind of mind control technique.
All this combines into a turd tornado. Mentally ill people use it as an excuse to kill more people, the government uses it as an excuse to spend more money and pass more laws and your grandma uses it as an excuse to say racist things.
I think if the media had been a touch more responsible we wouldn't be where we are. Frankly, I think the Ferguson incident was a total non-issue from start to finish and all the property damage and injuries resulting from the panic lies totally on the shoulders of the media. The Garner case (well, the second one) on the face of it looked a little trickier, but I was hardly surprised to hear of the outcome. I think all the folks beating the "new laws" and "harsh police tactics" drums will probably be confronted with the fact that most of our current police tactics are written in the blood of slain police officers, and are thus difficult to discount, particularly if you care whether or not you have any police around once you get the laws passed. If I got the idea that my life was worth less to the public than the violent felon I was trying to arrest I wouldn't even turn my shit in, I would just call them and tell them to come get it themselves.