Here are some impressions and thoughts on Black Lives Matter thus far... The authorities always like to pit groups against each other or a least watch gratefully when, say, the Tea Party waste its energy against Occupy Wall Street rather than the government. So I tend to bias in favor of most any political group that isn't too, well, political.
I've only been to one of BLM's events (to film). That was in mid 2015. I don't even remember if that was what they were called back then. They seemed transparent and friendly enough as I ambush interviewed the leader and questioned her apparent position that private Confederate flag displays should be illegal. They burned a Confederate flag in front of me...I got the chance to question everyone else's position that the burning should be illegal. Google "Confederate flag burn Ridley" to watch the vids.
BLM's primary grievance is presumably the large number of U.S. police shootings.... of folks who are black. That's about as legitimate a grievance as you could come up with ...and it's no real fault if they stick up better for people who look like them...than you do for people who look like you. That would not be my primary means of determining who to stick up for. But at least they're sticking up for someone as U.S. cops kill a thousand people a year. German cops only kill about four.
As for blocking roads, that's a violation of the Zero Aggression Principle and endangers bystanders. They should probably do some other thing as long as they're taking that much risk, like block a police station. However Martin Luther King did block roads...not by trying to stop traffic necessarily but by using them for massive foot traffic. Same effect. But we all like him why? Because he was victorious, ballsy... and his ZAP violations were limited. Also it's not his fault, or BLM's, that the authorities have made it difficult for folks to build new roads or alternatives to roads. Physically blocking travel would be very difficult in an established free society.
Regarding the attacks on cops... I haven't yet heard of a cop killing by BLM. Presumably some of the emerging guerrilla fighter types sympathized with BLM goals. This phenomenon also played out to some extent in Gandhi's India as well as Dr. King's American South. King and Gandhi were responsible for what they did, but not for what they opposed. And they opposed these retaliatory killings, much as BLM leadership seems to.
Dr. King favored some force-initiating government policies just like practically every human does these days, so when BLM does that it doesn't make them Mr. Burns. It just makes them a fairly typical U.S. civic group that's willing to do some ethically challenged civil disobedience, is larger and more discussed than most and which has more legit grievances than most. BLM grievances like dead harmless people ...sound pretty legit. Other groups' grievances like oh-my-God-some-people-are-smoking-marijuana...or oh-my-God-some-people-are-carrying-firearms-without-a-license...those are not legit grievances.
So those of you conservative folk out there...who listen to what I say a bit because you see videos of me attacking government spending in person... listen to this: If you're raising hell about BLM and treating them as the enemy, over the things they do which do not initiate force; if you are defending police activity in the face of BLM's concerns...here's what you're really doing. You are doing the bidding (bidden or not) of the big-spending government you supposedly dislike. All the perpetual half-staff-mourning cop-filating math-dismissing of yours is just helping your enemy-government at its most brutal and politically vulnerable point...its enforcement arm.
The reverse applies to BLM folk, of course. The government is their enemy - and yours - more than other civic groups are.