I am pretty sure I am not the only Mastodon admin who feels this way; anyone coming to the Fediverse should probably be informed that this is a reputation this particular software has.
If this bugs you then do something to clean up Pleroma's overall act and make the racist trolls know they are no longer welcome to use it.
Any offensive domain you come across could be running Mastodon, Pleroma, Misskey, etc. The behavior of individual servers doesn’t reflect on the open source technology they are using.
I guess it just so happens that offensive people prefer to use a more resource efficient technology. Not sure why that is, but I think it’s funny that people like yourself prefer crappy technology if it means that it aligns perfectly with your political beliefs. Just weird to think of servers in this way. As if NGINX could be political.
The original question was "What makes Pleroma different from for example Mastodon? Why would one choose one over the other?", and "Masto admins are less likely to cut you slack in a dispute if you're on a Pleroma because they see a lot of jerks using Pleromas" is a difference, IMHO.
I can't say I "prefer" Mastodon. It's the server that was there when I decided to start running one. One of my friends switched over from Masto to Misskey and seems to be happy with it but it was a lot of hassle to do the change, more than I'm willing to bother with.
Old-school Unix systems. Mainframes. BBSes. Mac vs. PC. Hondas sporting spoilers. F150s sporting certain bumper stickers and exhaust modifications.
In cases, this becomes a self-fulfilling prophecy.
For at least a signficant portion of the Fediverse, Pleroma use has come to be associated with a certain set of users, to the point that the servers are blocked on sight.
Which those seeking to join the Fediverse might care to take into account.