A: There’s a kind of self-selection going on where the people who join Mastodon are maybe more civil. But it should not be discounted that all the different servers, with their rules about hate speech and against harassment, are doing moderation work and acting as gatekeepers against bad actors."
I haven't used Mastodon yet, but content moderation is one of the hardest most time consuming problems they will have. I am doubtful that volunteers can provide the level of moderation needed in a full scale social network.