Which activist groups actually value being nice to other people.

Clearly, not the mainstream pro-SJ community. If you tell them to be nice, they'll throw "tone policing" and "respectability politics" at you.

"Anti-SJWs" are definitely out of the question, as well. While they seem to disagree with the pro-SJ side (You don't even have to be an SJ militant to be called an "SJW" by that lot.), they somehow seem to agree with the worst factions of the pro-SJ community that it's cool to ruthlessly belittle other people. If you tell them to be nice, that'll mock you about "rustled jimmies" or being "butthurt" or "triggered".