I enjoy jam music. I grew up loving Phish, Grateful Dead, String Cheese Incident, you get the idea. But man do I hate some jamband fans. I'm almost reluctant to call them fans, because they can be such a mixed bag. While I've met some great people and made lifelong friends on tour, I've ran into my fair share of shysters, ne'er-do-wells, and assholes. But the absolute worst are the gatekeepers.
I made a post in reference to jam band types about a year back, and I found your experiences very interesting, as mine have been almost the inverse of yours. (Though, it might be because I'm mostly talking about musicians here.)
Across the board, non-musician fans I've met are pretty chill, maybe a little basic bitch and/or hipstery at absolute worst.
All of the older musician fans I've met are super solid people. Maybe not the most skilled, talented, or cool, but always go out of their way to be helpful to others. The kind of guys who have a regular day job, play in local bands, host open mic nights at bars around town, actually work at venues or teach instrument classes, etc.
The younger ones, however, are some of the most pretentious, insufferable, unwarrantedly egotistical people I've ever met in my life. They're the opposite of gatekeepers though, more like evangelicals. They come in three flavors:
A.) Impotent Elitist Dickhead. A guy I know who falls into this category once went on an fuming angry tirade to me about how all people who aren't into jam band music are like that because all they care about is instant gratification and are literally too intellectually inferior to grasp how good bands like Phish are.
Lazy, thoroughly mediocre bordering on complete shit players whose entire musical mentality is literal coping and seething about the reality that people who put more time and effort in are better than them, even if their tastes might not be considered artsy and high-brow. Usually a stereotypical Redditor in terms of tastes in everything else. Basically, guys who took up acoustic guitar to get pussy in college then fell for their own bullshit over the years.
B.) Stoned Retard. Much nicer on the whole, but borderline useless. I've met people who have been playing their instruments for years who can't even begin to tell you what keys are where, and constantly have some kind of reference sheet in front of them. Music to them is basically just getting high as balls on various substances and fucking around with effects and whatnot. Generally cool and fun to hang out with, but immediately 180° and get really pissed if you have any expectations that they learn anything and/or not get completely wasted halfway though a jam session.
C.) Music Theory Autist. Actually talented, but has the mirror opposite problem of the first two. The kind of person who legit has a degree from Berklee or Juilliard, but expects everyone else to be on that level. Super aloof and difficult to work with, massive superiority complex. Basically the epitome of why people online give advice about "It doesn't matter how good or smart you are, you have to learn to be likeable to get anywhere".
Generally ends up going nowhere after years of work and shit-tons of money spent, because they refuse to accept that music isn't a math problem, and that having perfect pitch and knowing how to play every esoteric chord combination on every instrument is never going to magically make them not a weird, awkward autistic asshole that doesn't belong anywhere near a stage or a paying audience.
My overall theory with the elitism and abrasiveness we've both experienced is because of the improvisational nature of the jam band genre. Music (and performing arts in general) boils down to obsessively practicing something difficult to the point that you can do it in a way that seems effortlessly natural.
Most people realize that, but with bands like Phish and Grateful Dead, there's an emphasis on going off-the-cuff and just exploring where the music and the rest of the band takes you. Now, doing that well takes incredible musical knowledge and knowing your band mates extremely well, by way of shit-loads of practice. But, the fact that they
are improvising makes this the wet dream of every drug-addled narcissistic hippie retard in the world, fantasizing that all there is to it is: These guys just get up on stage and just like, let the music just flow through them, maaaaaan.
The rest are people who understand the level of work and talent involved, but use that to ego-trip that this is the highest level of musical skill. More straightforward jazz-type elitism.
Basically all the examples that you gave were druggie hedonists and stuck-up pricks getting assmad that filthy casuals showed up to their super secret cool kids club.