"Nigger Minstrelsy" as an authentic strand of theatrical entertainment stems from US C19 impersonation of blacks (stereotypically "Jim Crow") by white actors during intervals and from black banjo-playing street musicians. To this day there are hordes of deadly serious (and jolly good) banjo players of all colours who travel to conventions to play "nigger tunes" and defend the right to call them that because that is what black slave-descendant players call them. It is a definitive musical genre.

In England, "blacking up" has long been a feature of downtrodden workers demanding money (with or without obvious menaces) as a reward for musical entertainment particularly at slack times (c.f. Plough Monday) and in disguise so that the bosses didn't "blacklist'" them from employment when work again became available and the farmer turned to the latest wave of immigrant workers because they were cheaper.

Neither minstrelsy nor surreptitious street begging is acceptable nor PC in these "enlightened" times. But along with many another practice, they are features of traditions which alter constantly because that's what traditions do. Border Morris is particularly hybrid and this is a reason to examine its component antecedents, not to deny that certain elements do not (or may not) exist.

You do not, after all, ban historical songs about slavery, whaling or swashbuckling imperialism just because (unless Icelandic or Japanese) you no longer support these activities. You place them in context.