It's weird seeing it from Bernie Bros around the interwebs. If you are a Bernie Sanders supporter or at the least want to see him H2H with Trump in November (which I do), I can't fathom why you'd need to go there to take shots at a politician like Buttigieg. Seriously, wtf. He's got plenty of scummy, low-class fans like anybody else though.
I'm just not seeing it. Personally, I call him Platitude Pete, Wall Street Pete, Wine Cave Pete, Pete The Cheat, etc. It's all based on his policies (or lack thereof), his empty rhetoric and lack of integrity. Nothing about his sexuality. I almost forget that he's gay since he doesn't usually mention it and he's so straight acting.
The only homophobia I've seen is from that idiot Klobuchar supporter who caucused for Pete because Klobuchar wasn't viable and then wanted to take back her vote when she found out he was gay and had a husband (it was later reported that her vote ended up going to Warren). But I can't put that on Klobuchar either, even though I don't like her.
I'd like to see some data to support this, but my hunch is that the more moderate candidates like Klobuchar, Biden, and even Pete himself, have more people with homophobic views, who are more socially conservative and less likely to support same sex marriage, than Bernie and Warren do.
But if you have seen genuine homophobia from Bernie supporters, then yes, that's completely unnecessary and counterproductive and like you said, EVERY candidate has some scummy supporters.