The terms white and black were created hundreds of years ago to describe differences in skin colour and superiority. A lot of people identify with being black or white, but there are not many people who actually have black or white skin. The terms also don't cover people who have heritage from multiple continents.
I think everyone should be able to identify however they want and this is in no way criticising the BLM movement, but I am uncomfortable that everyone should be expected to accept the terms white and black and be identified as such by others.