What this thread so beautifully illustrates is, as I have pointed out elsewhere, that it is province of moral realists to work against injustices such as slavery, Jim Crow laws, gender discrimination, laws denying same-sex couples the right to marry, etc., etc. The moral anti-realists obviously cannot think of any rational reason to try to correct injustices. There are no such rational reasons under the guise of moral anti-realism. Injustices and bigotry would flourish under moral anti-realists.
Equally unflattering, apparently moral anti-realists just have no ideas, are relegated to repeating pablum ad nauseam. It's like belief in determinism or disbelief in free will--it encourages complacency, inertia, and easy immoral behavior.