So my understanding of the legal requirements of terms of service (which are generally not strongly enforced either way) is that if it changes you just have to sign the new one, or decide that you disagree enough with the changes that you won't sign it.

To the "extremist" point, I have to say I really don't see it. Changing "master" to "main" doesn't seem like an extreme political position to me. Extreme would be someone murdering protesters, tweeting someone chanting "white power", or hanging black people from trees in Texas. Those are pretty easy things to not want in your society. The same with people setting businesses on fire or brandishing weapons in public. But I don't see how someone trying to reduce their harm externalities by changing words is particularly extreme.

This may come down to the difference between the ideas and the people holding the ideas. I don't think there's anything wrong with the idea. I think we can both agree that we wouldn't want people harassing each other for either making or not making this change, as anyone should be free to make whichever decision they feel is right. To the extent that the "left" is the cause of the harassment, I can agree I'd rather those people deal with this more calmly. But again, they're not the ones murdering people.