I totally hear you on that, though I'd add that the overly zealous are invariably new to it. In-group policing among vegans tends to moderate that vitriol within a few months.

I wonder (now that I'm thinking back on instances of "the new and the loud" I've known in my decades) whether some adopt veganism /specifically/ to have an issue to be loud about. When that behaviour is rejected from both the in and out groups, they move on to some other issue. Certainly lines up with some I've seen... I dunno, just spit-balling here.