I would argue the major problem with the knee taking is that any gesture loses most of its impact/meaning if it is mindlessly repeated ad infinitum.
It just seems kind of insincere at this point. Yes, they kneel every week, but how many actually do more than that? Especially the white guys. It's an easy way out of doing some actual work. "I can't be a racist, I kneel before every game for a few seconds!"
They are in a somewhat difficult position to stand up for anything though, seeing how most are sponsored by a shoemaker that employs little kids, or have owners that hold modern day slaves, or big oil barons, etc