Have you actually seen an early Irish harp, like the one in Trinity College Dublin or those in the National Museum of Scotland? They are nothing like a revival-era folk harp, and weigh several times as much - the frame is a great big lump of oak, you would not take it anywhere without a horse or cart.

We know a lot about the tune, back to around 1700; there is nothing "typically Irish" about it since it was commonly used in England and Scotland before there is any record it in Ireland. It's obvious where Campbell got it - Burns made it hugely popular and it had been reprinted and circulated many times all over the British Isles. Broadside publishers didn't need to print the tune: they'd just name it, as "Banks of the Devon" - any literate singer from Cork to Lerwick would know what was intended. (Burns was first published in Ireland in 1787).

A harp would be no sort of disguise at all. There were very few harpists at any time and anybody who knew anything could name every one they were likely to encounter. And if any priest actually managed to learn the harp well enough to pass as a pro, we'd know about it.

I have an early edition of Campbell's poems where the editor says who Campbell actually had in mind - an Irish exile from the 1798 rising who he knew in Germany. No 17th century bishops involved.

There can't be many songs with such a well documented origin which so many ideologues are determined to ignore.