Where I've encountered such obnoxious gatekeepers in other fandoms, I've taken to calling them the One True Fans. Some basic tenets of being a One True Fan:

Any fan not from the exact same demographic as you is a Fake Fan, and Fake Fans are the enemy.

Only the oldest material in the canon counts. The rest is Objectively Garbage for Stupid People.

The creators of the source material are evil sellouts, and Hate the Fans. The creators are also the enemy.

Any progressive messages in the older material don't exist They just don't. Any progressive messages in the newer material are "forced SJW crap."