@mcepl: I completely agree with you that we shouldn't waste time with this. I would be better not to dig into the discussion about "master-slave" terminology. IMO we don't even need to go into that as the problem here is more substantial:
This case can create a very problematic precedent i.e. _on can modify (even drastically) a well established terminology based on "pseudo-reasons", political opinion or ideology_.
IMO this should be stopped and prevented as soon as possible for all sake. On the other hand, I believe the @vstinner is a rational person and he is able to give _rational reasons_ for his decision which other could challenge as "potential offensiveness" of language is not an argument.