It's not a big deal, but it's not a trivially small deal either. It's sufficiently annoying that there had better be a good reason. In the case of "slave", there's at least a good argument. "Master" is ridiculous. You cannot speak this language (or Spanish, or Italian, or any other latin-related language that I know of) without that word. We've got master's degrees, master copies, Let It Be (Remastered 2009), and mastery. It has no reason to die, and it will not die in our lifetime. The master->main pain is just performative pain for its own sake.