I think Irish drums (whatever you want to call them) are criticised too often. Most of us folkies are only fair musicians (at best, ok. some are great but many are not but can still be enjoyed), and it can look very self aggrandising to put others off or down, and I well remember a rather precious actor-singer telling a very good guitarist that he found his playing "rather distracting".

I think the safest course is to say in advance if you do or don't want people to join in, and to warn them it there are unusual things coming such as an arrangement with a chord that is not the usual one, or an accelerando on a particular part of the song, or if (like me) you do the "Wild Mountain Time" in 4/4 rather than 3/4.

By and large I think of folk music as participative. It may be necessary to vary that but it is probably better to be cautious. Offer to tune the guitar that is driving you mad. Get someone else to tune the banjo that is driving you mad. Point out that you are playing a recorder in medieval pitch and that it is NOT a semi-tone off modern pitch. But if you have to ask someone to stop you have to - once you are sure that you are not being precious and self-important. SOmetimes you have to. But examine your conscience first.

he story that started this thread may well have been one of the occasions when a firm stand was essential - but it could (with the benefit of hindsight, which is always easier) have been avoided by saying in advance that you were doing a song that was not in strict tempo and so was likely to be better without rythm accompaniment. The reaction to such an ADVANCE announcement would warn the alert if they were pushing into a session or being self-important (which some, but not all, unaccompanied singers can be). One reason I tend not to do unaccompanied songs is that you do have to be doubleplusgood to make them a good experience for the listener(s).

Be careful. You probably were. If you were, then you did what you had to do. But in many cases it is not necessary to exclude accompanists. I know one "jam session" (so advertised) when an excellent guitarist thoroughly surprised me by joining "Haul away for ROsie" (which a friend and I were doing unaccompanied, like most shanties, and in B as it happened) and the blues feel to the sequence he added put a whole new light on the song for me and I thought it was great. I might have said that shanties were usually unaccompanied and I woudl have missed a very enjoyable experience.