The greater online underground music communities as a whole, including but not limited to extreme metal, dungeon synth, and punk rock. This especially pertains to DIY/independent subgenres and musicians. A lot of them are based out of facebook, but there are also outliers on dedicated forums such as MetalArchives. Im sure sites like RYM and reddit (no surprise there) are havens for this as well. Their antics vary from alarmist cancel campaigns against musicians/bands they find politically distasteful/problematic, or discussion about really dumb shit like questions about how to properly tour cross country in an astro van with a dog and six other members while subsisting on gas station food exclusively, or trying to find pro-feminist LGBTQ2S+ friendly venues in the middle of BFE flyover country.
Dungeon synth in particular is rife with alphabet people, autism, and unwarranted elitism/gatekeeping. I've seen so much bizarre shit from this scene that it soured me on the genre entirely.
I used to curate screenshots from a bunch of different groups but it finally got to be too much and I abandoned the project because it made me legitimately MATI.
A number of the people involved in these "scenes" could easily have their own threads here, including Kim Kelly (far left former "journalist" for Noisey who tweets all day, has a crab claw hand, and slept with the entire NYC metal scene), Morrigan (admin for Metal Archives and, according to a brief search here, also a user/former staff on SA), and the entire staff of MetalSucks (notorious crybabies who routinely try to "cancel" bands for trivial slights).