Unfortunately, some people, musicians or otherwise, are just jerks.

I just returned from my first time at a week-long event, where much to my surprise, I found that people playing one type of music were rather arrogant and snotty, while another group playing different stuff were perfectly friendly. (This is all folk music, mind you.) I am not a good enough musician to really participate in even the friendliest instrumental session, but did participate in about four different song circles, where I managed to get in one song at each. In all but one case, where strict rotation was observed, the singing was dominated by the people who already knew each other and were known to the person leading the circle.

I guess that is only to be expected, but it has certainly made me appreciate the inclusiveness of my "home" chantey session, which is pretty much the only one I have attended regularly. Chanteyranger spends a good deal of time trying to make sure that shy newcomers have the opportunity to lead a song if they want to, and sometimes moderating when the regulars all try to sing at once. It seems to me that it's really important to have someone actually running the session, rather than just letting it grow organically and hoping for the best, and it's really nice if the leader has an eye to including everyone.