They don’t ban Sith cosplay, and the article asks why.
I think the line is pretty clear to me. I used to RP a dark-side Sith lord a whole lot. It’s in the galaxy far away – it’s been transformed changed, removed from the literal Earth history. That transformation creates the magic circle for play. Hydra isn’t metaphoric enough.
Sith are vague metaphors for Nazis. Hydra are not-even-metaphorical Nazis.