I'm not trying to argue against it, I think "slave" branches make no sense anyway, but to GP's point BitKeeper didn't enslave anybody, just used the word.
If we believe we should remove allusions to negative things why are we ok with "kill", "orphan", "evict", "bash", "cut", "isolate" etc? What is special about that terrible concept that we should stop using the word even when not applied to people at all?
The point of bringing up Bitkeeper is as much because why use a word divorced from its original meaning at all? "master" wasn't an explicit choice by a git maintainer, it was inherited noise. When confronted with where that choice came from, in finding it wasn't a choice but a bad legacy, the git maintainers generally agreed it might be nice to pick something that made more sense as a choice (rather than bullshit noise from a practically dead and gone upstream project) and after much debate "main" made sense as something a lot of people were using anyway.
That's what is "special" about it, that it wasn't special. It wasn't chosen. It was just a stupid inherited default that didn't make sense when questioned.
It was never an intentional allusion to a negative thing, it was accidentally a negative thing causing real people some harm, and it was easier to fix than to justify why it was a negative thing in the first place.
If we believe we should remove allusions to negative things why are we ok with "kill", "orphan", "evict", "bash", "cut", "isolate" etc? What is special about that terrible concept that we should stop using the word even when not applied to people at all?