For what it's worth in this erudite discussion, "context is all" in my opinion.

A good example is on YouTube right now. I won't add a link as I don't want to frighten the horses! It's a performance of "Look Out There's a Monster Coming" by the Bonzo Dog Doo Dah Band, done on TV about 40 years ago. For those who don't know their oeuvre, the song's about a little bloke who attempts to make himself attractive to ladies and succeeds only in turning himself into Frankenstein's monster. In the clip, the band are all blacked up, and limbo dancing is also involved. In theory nothing could be more stereotyped and offensive, but it's actually hilarious and a total p*ss take, like so much of their stuff. I imagine Charles Atlas type ads, 1960s light entertainment TV and particularly "The Black & White Minstrel Show" were primary targets.

As another example, the wonderful Mitchell and Kenyon films unearthed recently show a carnival procession in a UK northern town around 1900. There are about 50 people dressed up in "darkie" outfits, complete with banjos, top hats, etc. etc. These people are now just shadows on a screen - branding them as "racists" doesn't get anybody very far.

To get back to the actual subject, I honestly think a lot of the blacking up by Morris sides started with the Shropshire Bedlams, and has become "traditional" as lots more Border Morris sides have started. So it's an Ancient English Tradition which dates back to about 1974. (But to be fair, my Dad remembered my grandfather talking about the Lincolnshire Plough Monday tradition which involved facial disguise and demanding money with menaces).

The Britannia Coco-Nut Dancers are another kettle of tea entirely, and anybody who interferes with them (ooer missus) does so at their peril.