Lemmy really needs a way to filter sensitive communities so content like this can be hidden away from feeds/federation unless users explicitly want to see it.

This is really the issue. Having scat appear in the 'All' section of the website probably isn't very appealing to most current or new users. It's not that we should push it to another instance or mark it NSFL (since that's not really what that tag is meant for), but that it should just be marked as a sensitive community (by a site admin, or perhaps by the community admin), removed from 'All', and have a confirmation screen whenever a user tries to enter the community. The "site who shall not be named" had a similar feature.