The average BLM supporter thinks racism = ethnic prejudice so they would mean ethnically prejudiced people. Instead of pretending to think there's confusion over whether anyone values black lives, they would be telling the truth about their desire to prove it's impossible to rule out warfare and killings against ethnically prejudiced people.

The average BLM supporter is also ethnically prejudiced, and also pretends humans aren't one race, which is the real racism. They would rather say "black lives matter" because if they admitted "racist lives don't usually matter" they'd be admitting they're in a pointless fight killing people just like them and getting killed for the same reasons they kill other people for.