Critical Theory according to Horkheimer isn't value neutral at all--practically his only criterion for what makes something Critical Theory is that the student is embedded in the quest for social justice.

As to whether CRT is Marxist: given that you make a pretty major category error in using the claim that BLM is a Marxist organization to support the idea that CRT is, because you haven't established that BLM is an expression of CRT, I think I would want to see some evidence from you.

You can certainly trace an intellectual lineage from Marxism through Critical Theory to Critical Legal Studies and then to Critical Race Theory. But at each step, part of the previous lineage was rejected or elaborated (otherwise there would be no need for a new name!), so even knowing that there is such a lineage is not enough (and you did not trace the lineage in your argument).

So, how about an argument? If you mean the leaders of the intellectual movement, quote Bell or Kimberle or Delgado or someone. If you mean the broader societal trend inspired by CRT that the left has no name for--I'm fine with calling that CRT too, as long as we're all clear on what is meant--then the BLM organization is only a small part of that whole effort, and furthermore, you didn't even support that BLM was Marxist. Show your work! It makes it much easier for other people to know whether to believe you.