I think it's sensible to to do this by considering the extremes and working in. There's bound to be an area in the middle where it becomes iffy, and put in the stake somewhere there- remembering that others will place their boundary elsewhere. That of course isn't to say that all boundaries are equal.

A friend who is mostly unacquainted with folk music went to an English seaside town a couple of years ago, and was pleased to find that there was a folk festival on. He went into a pub, and found a singaround, which he listened to. Until eventually it dawned on him that this particular session was a BNP group, singing hunting and whaling songs, songs glorifying war, songs in which a word that began with N was prominent, all as far as he could tell traditional, and to the exclusion of possibly non- controversial subjects.