I think you continue to conflate the sentiment with the organization. The founders of BLM are Marxists. They say so. Marxism is dangerous because it values outcomes over process, and thereby always ends up with bad outcomes. If it can't happen here, it's because people resist it. I am resisting it. To not resist it because it won't happen is circular reasoning.

Marxism is also relevant because racism is a particularly powerful form of classism. If the haves need a lower class to exploit and exclude, the discovery of one that threatens their genes and can be easily identified on sight is too good to be true. So, naturally, physical difference becomes a basis for class.

The Marxist idea that history is largely a struggle between haves and have-nots leads to the idea that the only good society is a classless society, achieved by any means necessary, including equal poverty as a replacement for unequal wealth. A classless society is not racist, because in that context, a race is a class. So, many anti-racists are drawn to Marxism.

Marx is very interesting. I suggest you give him another look. Structurally, exploitation is exploitation. The special horrors of chattel slavery are icing on that toxic cake, but the privileges of the haves are the same no matter who the have-nots are or how badly they are treated. I can understand Black people not wanting to be lumped in with the Proletariat, as their suffering has been unique and unrelieved by the progress of the working White man. But racism does not motivate White people; classism does. Racism is just the most convenient implementation.

For your preference for "something new" to gain traction, you will have to come up with what that something new will be. Otherwise, it will be tyranny. I'm sure you can see how that possibility might be scary.