I have seen a lot of people who've decided "I want to play jazz" based on the idea that jazz is "sophisticated and hip" - but with minimal knowledge of what "playing jazz" actually consists of. Failing to understand that there's a repertoire (really, several repertoires) is a common issue. I remember a female singer who decided "I want to sing jazz" but she wouldn't listen to the famous singers, pick some common tunes, learn them in common keys - oh no, she decided that her entry into being a "jazz singer" would be with some oddball show tune that no one's ever heard of - an incredibly obscure torch song. Of course, it was complicated as all hell, so the ordinary pickup pianist didn't want to have anything to do with it, and she got all upset because no one wanted to participate in HER idea of "being a jazz singer".
Especially if you are attending the standard open or semi-open jazz jam, you can expect there'll be a certain repertoire of tunes. If you want to try out something oddball, you've gotta bring charts or at least chord sheets (unless it's another variant of Rhythm Changes or something like that). That's the way this thing works. In my visit to the jazz jam the other night, NO I didn't bring charts or books or an iPad. I also was pretty certain there'd be someone I could look over their shoulder (there was) and I was pretty certain I'd have played all or almost all the tunes many many times over the last 45+ years (also true).
But for an open jam, DON'T be that guy who calls the weirdo tune, that no one knows. And don't be the guy who stands up there and fumble-farts around, loses the time, and makes everyone look at their shoes till you finally grind to a halt in the 22nd bar of a 32 bar tune. I mean, you can blow some clams, and if you explain you're getting started, you'll be cut some slack, but at least have SOMETHING under your belt. It's far from disastrous to refer to a lead sheet or chord chart; that's not what I'm talking about here. I'm talking about the norms of how jazz jam sessions work, for the best results for participants and listeners.
If you want to focus on unusual tunes, go start a band. I know a guy who's focused the last several years on the music of Tadd Dameron. (some of Tadd's tunes are in the "jam session canon", but not many, and there's a ton of material out there that few have ever heard). So, he formed his own band.
If you want to "just jam freely, without being restricted by things like song form or accepted repertoire", then you need to form a group to do that. If you're a genius like Ornette Coleman, it might result in some really interesting stuff. If you're tripping and high, it might result in something like some of what the Grateful Dead did. I'm going to bet that it won't be either of those.
Structure in music is good. People who are successful at stepping outside the structure, either briefly, or in an extended way, are 99.999% of the time the people who have mastered it within structure, and then stepped out. (Listen to Coltrane, or Rahsaan, or Dolphy, playing a standard ballad.) People who reject musical structure from the get-go are rarely successful.
Pretty common experience with singers, actually. They inquire with me, I send them our list of 120 jazz tunes we do, tell them 'we'd need 18 for a gig'....and then either hear crickets back....or they at least reply with 'I only know three of those....'
To which I reply...ok, so you would need to learn 15 more'. I never hear back from 50%, then 25% say they might be willing...and the other 25% say 'I DO do THESE songs' then send a list of songs which are not jazz (show tunes, or just some chill/groovy pop/rock).
The KEYWORD in Turf's reply here, to me....is....CONVENTION.
Jams HAVE TO HAVE some Conventions employed to keep things from going off the rails.. The ones I was regularly part of had the 'right to left' convention - calling out of the tunes went right to left depending on how horn players were positioned, then rhythm section had an order too.
Solos same thing.
Next convention- you know the tune ? If not, cam you sightread the head ? if not, you wanna take a stab at soloing the changes (by READING THEM OFF A CHART, of course)?
If your answers to all were 'no'....then you sit the tune out. Period.
There is NO available option for -"I don't have music, I don't know these songs, I am not a moderately accomplished sightreader.... but I am just gonna let the spirit MOVE ME, have no PRECONCEPTIONS, and give it my 'best shot' ".
That is just 'Unprepared' . You shouldn't be there. You aren't ready for the Jam.
No 'full marks' for that. I see no work in that, no desire to have oneself ready, no desire to learn any lessons from the previous experience.
There is no theoretical or philisophical musical 'debate' to be had along the lines of 'hey, man, the Creative Force should NOT be shackled by these rules'.
There is no way one can logically start pointing fingers at the jam organizers and say 'those guys/gals aren't cool...go find someone who IS.'
Like Turf said, if your bag is "not interested in learning 100 standards, not interested in jamming on 'em in (what you perceive as) some highly-controlled environment", you just wanna blow, unfettered...
Find yourself two or three other folks who want to do the same....and just have sessions with them.
Or stop playing with people altogether....and stick with the high tech instrumental karaoke...