When the basic premise of the argument is that white Americans are born irredeemably flawed[1], you're unlikely to win many white supporters other than the most guilt-ridden.
I suppose the tactic is to impart as much guilt as possible. But that doesn't make the argument a good one.
[1] https://twitter.com/DisrnNews/status/1266857347567190016
Why are they doing more harm than good? Because, after a claim like that, the conversation is over. There's absolutely no point in talking to someone who makes claims like that. And it makes you less likely to be willing to talk to the next person, either. So the net amount of whites willing to learn and talk about race and racism goes down when people say stuff like this.
(It's also factually untrue, blatantly unfair, and bigoted...)
The tactic is to get people to actually listen so that they might agree its an actual problem and then actually do something about it.
To do so is scapegoating and white Americans have every right to resist it.
There's been no penance. There's been no justice. And people aren't even asking for that, they're asking for a seat at the table and a chance to play the game, which is STILL constantly being denied. Its not scapegoating, its fighting against systematic oppression that you yourself continue to support.