They’re a “gang” like any large group of fans for any band/performer is a gang. One could say Beliebers are a gang, especially when they mass attack someone on Twitter. One-on-one you’re going to find good folks and bad folks throughout. It’s masses of Juggalos, like any large groupings of drunk assholes, that can be a problem.
The biggest issue with Juggalos is that the band they support comes with a bunch of culturally incompatible bullshit like scary clown makeup, not bathing, drinking Faygo, (seriously awful soda) carrying hatchets, and acting like uneducated idiots. This is all purposeful, of course. Mass quantities of alcohol and drugs come with that, which naturally amplifies their behavior and leads to some really bad decisions. Think of the early 70’s punk movement, but dumb everyone down by 50%.
Unfortunately, unlike punk, ICP has built a profitable industry around their fans unifying them and keeping the cult going for years past its natural end date. They’ve been able to successfully tie their fans into complimentary media like backyard/underground wrestling and “horrorcore” films, amplifying the impression that Juggalos are poor trash, further separating them from mainstream society. Tribalism at its finest.
Mostly, the FBI assessment is correct. Juggalos are a loosely affiliated gang of idiots that are prone to committing crimes, mostly of a petty nature, but drugs can make things turn violent.
Also, ICP makes terrible music.