We know that liberals don't really believe that though. Otherwise they would be fine with a nation wide popular vote on issues like abortion, "gay" marriage and illegal aliens. IOWs their ethics are entirely situational.
Liberals would be happy enough with a “new slavery” as long as it was based upon the mores they liked. All the popular media flouting of traditional families and white people would never be happening if they stood on divine principle rather than upon perpetual class warfare.