The word 'scab' had not occurred in the thread until now. It is relevant, but in precisely the opposite way that you imply.
Where do employers get scabs, literally? From the ranks of immigrants, minorities, and less well-off workers. It's a poor anti-racism that defines the holders of better jobs-- against which literal scabs are directed--as the problem, because of their admittedly imperfect attitudes. Defense of labor standards means going against the immediate material interest of less well-off workers, often of oppressed minority groups. That's what the labor movement has always been about. You create, defend, and try to continuously enlarge the sphere of higher labor standards. This is really elementary.