For me there are two issues, firstly I think football is better off being non political so don't endorse or oppose any causes, that's not to say we don't tackle racism within the game we just don't support political groups like BLM.
Secondly taking the knee is an american protest let them get on with it. If our society had anything about them we should have been out on the streets over the Windrush scandal or when Smiley culture was stabbed to death allegedly his own doing.