I used to be involved with a composers' consortium. The organization was comprised of several of my friends. In the beginning, everything was alright, because there wasn't a lot to manage at first, but at a certain point, I decided that the leader of the group was mismanaging things and it would be better for me to go it alone. So I dropped out. That was a little over a year ago.
In addition to being a composer, I am also a professional web developer (kind of new to the profession, but not inexperienced in the work place, generally). I have stayed in touch with the composers in the organization I mentioned above, and I mentioned to them that I could redo their website and make it into a full-blown web application with lots of useful archiving, planning and management features in the backend. Initially, payment was brought up in a very loose way, and I said, just give me what you can, this is a favor I'm doing as a friend. I tried to gather requirements from them like they were any other client, but the mismanagement issues seemed to crop up again. What I mean by "mismanagement" is basically a lot of buck-passing and general negligence, not being decisive, clear, and I would be left waiting two or three weeks with no contact, etc. So I got the (self-appointed) "president" on the phone and asked him if I could just get started with it because I was really interested in the project, but I didn't want it to drag on forever.
I shouldn't have done that. Without clear requirements, and knowing I wasn't getting paid, I figured I would just have a lot of creative freedom, and when I was ready, present them with a series of demos and begin the more iterative process with feedback, etc.
What's happening is horrible. I have about 200 hours in this project. So far I've presented them with one demo. Most of the members are on board with the process, more or less, giving comments and participating, but the self-appointed "president" of the organization is now swooping down with a lot of criticism, and in some cases being rude in his criticism about things that he clearly doesn't understand (most of his criticism is based on strong opinions about things he thinks he knows more about than he does). Many of the members don't agree with him on the direction the site should go, etc. And it's clear that he hasn't read most of the group's comments and is dictating what should and shouldn't be done. On top of that, he is all but unreachable outside of email because he is vacationing in Europe for two months while this is all happening.
So, it's turning kind of ugly. What was once a really interesting project to me has turned into something I really wish I could just drop out of, but I don't know if I can do that without burning any bridges. Many of the members of this organization, most of which are my friends, are really excited about the new site, but tension within the group is really making this hard for me.
I think I know what mistakes I made getting into this situation so I can avoid it happening again, but how do I fix this now? Should I try to help them resolve their issues? Should I tell them it's not working out, but give them what I've done so far? Should I just soldier on and get it done on principle?
What is the most peaceful and professional thing to do in this situation?
Update: I ended up doing a version of Monica's answer, except I also requested a change to the terms. In their last response to me, they asked if I would just like to rejoin the group. So I let them know that what has happened so far wasn't what I had anticipated going into it, that if they wanted to continue on with the project, I could take a (modest, 25% of a fair market price) payment, either in cash or in trade (they put on concerts and do recordings and I could have one of my compositions done through their organization). So, if taken in trade, at the very least they can pay me back over time. We'll see how that goes.