::::There a whole section on the Scotch/Scots topic at Scotch-Irish American#Scots-Irish as a general term and the subsection "History of the name Scotch-Irish". Seems to be explained pretty well. Looks like people have gone over the topic repeatedly on the talk page there. There's an interesting quote in the section Talk:Scotch-Irish_American#More on Scots-Irish vs Scotch-Irish. Apparently the use of Scotch for people, while offensive in Scotland, is normal in Ulster. Personally it doesn't matter to me which term is used. It's an interesting example of conflicting usage between America and the British Isles, and apparently between Scotland and Northern Ireland too.