This is their thread, as you can see they've already collected several testimonies about this form of exclusion:
They don't specifically mention Masstagger but it's pretty obvious that's what's been happening: Bardfinn and other SJWs from /r/AgainstHateSubreddits petitioned Nathan Beam to add /r/truscum to the Masstagger blacklist, and then tagged everyone in /r/truscum as a "far right Nazi" to stigmatize them and smear them. Now all the mods of the other subreddits that use Masstagger are pre-emptively banning /r/truscum members to prevent them from participating in their subs. s/Introductions on this site is full of stories of people realizing they were pre-emptively banned on other subreddits and having no idea how or why this happened. Most of these people have never heard of the Masstagger plug-in and have no idea they were tagged there and added to a blacklist where they are politically profiled as a "far right Nazi" for having non-SJW opinions.