The "some" in that equation are of the vocal minority, ultra-radicalized types. I'm sure that the overwhelming majority find them just as disgusting and counter productive to their movements as everyone else does. To say the entire movement is like the worst of the group is to say "All vegans want to force pregnant women to give milk for Ice Cream." A lot of animal rights activists hate PETA for making them all sound like loonies.
While indefensible by any means, this is the by-product of how the media handles these cases. There is outrage, and most of those outraged just want to peacefully say "HEY! There's something wrong here and we want to have a conversation." Which is met with either "Ehhh...No!" or "Youse guys is stupit because we have no problems," particularly from a certain news organization who's head is currently on trial for sexual harassment. The extreme opposites butt heads, and the middle ground is forever lost, and a conversation is never had. This leads to the angry, disillusioned types to attack police officers. If we really want to stop this kind of retaliation, something needs to be done.
Which comes down to my rant about all this, every time there's a huge problem, certain groups likes to not only sweep it under the rug, but they then turn the perpetrators into the victims. When it was revealed there's a rampant poverty problem in this country, instead of having a conversation or giving long term compromises to help, the upper upper upper class started whining about how it's unfair that everyone hates them. When certain uber-conservative, ultra-fundie religions are exposed doing something UnChristian, instead of saying "sorry, the US is not a religious autocracy, and freedom is a two way street," they whine about how their freedom to take away the freedoms of others is under fire. And in this case, when there's systemic racism in Podunk police departments that leads to police brutality, instead of saying "Holy crap! This needs to be fixed." we get either awwwwww you hate the police or awwwww you hate white people. Really? There's no nuance. There's no subtlty. I'm sure that most who agree that there are problems also know that most police officers and most law enforcement aren't the corrupt jerks that manage to screw something up so badly they make the news. But we'll never hear it because some talking head won't be able to sell some book somewhere.
The problem is that something should be done about things. It isn't a righty lefty issue, but certain hateful media outlets, not to mention tin foil hats online want to spread American Exceptionalism (a frightening ideal I'll rant about later), hide the fact that there are problems because they (gasp) could very well wind up taking indirect blame for it, and then vomit the blame back on anyone who disagrees with them. And frankly, we should not be surprised that those who are that disillusioned wind up going insane and trying to kill people. It's horrible, it's destroying the world of good peaceful protesters are trying to accomplish, it's giving Bill O'Reilly more credibility, and it's leading to violence that could totally be avoided if we just calm down, let cooler heads prevail and stop listening to the kinds of jerks on a network that makes money off of the suffering of others.