There are lots of nice people in FP circles and nobody ever said there wasn't. But I think the author is taking the use of the word "arrogant" much too literally--its users generally don't mean arrogant, they politely mean asshole.

My sense, from spending a decent chunk of time in a couple different communities, is that they don't do enough policing of their jerks and that that makes itself most apparent to novices rather than established people. Many programming communities don't handle jerks well, for a host of reasons around social standing and conflict avoidance, but of the ones I regularly participate, I don't think a guy like Scala's I-think-I-can-use-the-adjective-"infamous" Tony Morris--though granted, he seems to wish he was Haskell's Tony Morris--would be tolerated past weeks, to say nothing of years.

I really like functional programming. But I find that notions like "shared-immutable programming" are more accepted by people who've been burned by the more socially toxic sections of the universe. The rebrand helps remove the association with the jerks, and that should speak to the impact of those jerks.