I just read this article on New Discourses and I think Lindsay misses the mark a bit. Not that he’s wrong about their central conspiracy theory (although he left out another key conspiracy theory - The ‘Epidemic of Police Killing Exclusively Black People’ is a Myth) but that he’s failing to mention a way in which BLM’s narrowing and exclusion is adversarial and paranoid.
He quotes the Black Liberation Army from 1975 (emphasis mine):
[A truly representative] democracy does not exist in North America, bourgeoisie democracy is essentially the dictatorship of what used to be termed the “national bourgeoisie.”
[…] the influence of corporate wealth on the politics of bourgeois democracy is merely an extension of private property’s traditional influence and control of the so-called democratic process.
[the democratic process under capitalism] is a means of mass diversion, designed to keep the powerless classes politically impotent while at the same time fostering the illusion that real power can be gained through the electoral process. Black People should know better. In a nation based on the false principle of majority rule we are a marginal minority and therefore our right to self-determination cannot be won in the arena of our oppressor.
If you remove the overtly Marxist anti-capitalist elements and change the target audience to be “the detached middle” (a-la Hidden Tribes) rather than “black people”, you’re left with something that sounds an awful lot like the standard “down with the duopoly” line.
The grievance here is one of exclusion from the political process, lack of representation, control coming solely from the extremes (or in the quotes above, from the bourgeois whites).
BLM is taking what could otherwise be a unifying experience for all those frustrated by the political and economic exclusion in this country and wrapping it in a race-war narrative, thus supercharging it for one race group.
An added effect is that this mantle is “owned” by racial minorities, rather than opening the doors to letting in a larger coalition of those who are excluded from politics. I suspect very strongly that if the suggestion was made “to BLM” (insofar as that’s a thing) to drop the race angle and the Marx angle and hear out a plea for unification against a greater enemy, they would be loathe to cede any of their hallowed race-war ground.