It's socially acceptable to hate / slander fraternity members (see the rolling stone rape case,) but it's not socially acceptable to hate hipsters, only to casually poke fun at them.
Just an observation, frat houses do focus very heavily on mob mentality, while hipsters are just a trend group. No one is going to get lectured by their fellow hipsters about being insufficiently loyal to the hipster brotherhood. Hipsters don't organize and intentionally seek to forge mob mentality and loyalty obsession. That is a significant difference just considering human psychology.