Many are the very shoes scrapings of society.
The ones who have failed to achieve any of the greatness they assumed would just fall into their laps so now they're angry with the world. They're especially prevalent in such ill-defined protests as this, as they know they hate "the system" or "the man" and they know that their own lack of success must somehow be blamed on them, they just can't pinpoint exactly what the system has done to them.
So once Twitter thinks for them and tells them "the system" is somehow racist, it's the perfect chance to show their anger. Perfect time to smash brick up and fudge up everyone's day because there's finally something they can finally pin something that wrong on "the man"
Unfortunately, the argument doesn't stand much scrutiny. Ask them precisely who the racists they're protesting against are and you'll get some loose concepts but no actual people. They're protesting against a racist government - ask them which member of the government has shown themselves to be racist and they struggle. They're protesting against Officer Chauvin - well he's a few thousands miles away, facing murder charges and has done nothing to give us reason to believe he's racist. So they're protesting against the police - surely they're racist. Again ask them to point out a racist policeman and they can't. We only have one policeman on this forum that I know of and he's definitely not racist.
But, but gammon! Brexit! Racist! Well. I suppose Brexit could possibly be viewed as racist in some kind of very skewed dislike of mainly white, privileged people from a disparate set of 27 countries.
They're the results of what social media has done to damage proper discourse. People who are (just about) able to speak in slogans and abstract concepts, but unable to apply them to the real world to which they cannot relate.