If I found out a racist or sexist forum was using Discourse I’d be disappointed but there isn’t much I could do about it besides avoiding it.
That’s the nature of software, you can’t put it out there and let awesome people use it easily without also allow less awesome causes to use it too.
I would not go out of my way to help them with support. In the past I’ve even ssh’d into people’s private installs of Discourse to help them diagnose problems. There’s no way I’d do that for a forum with toxic content. They’re on their own.