This has alot to do with hating the Brits and their continued occupation.
Here's a quote from that site.
"Oh here's to Adolph Hitler,
Who made the Britons squeal,
Sure before the fight is ended
They will dance an Irish reel."
Not that I support IRA or Irish people who gave refuge to Nazi's after WWII, as far as I'm concerned they can all burn in Hell. I'm glad you brought up this thread and I would love it to be discussed more because even being Irish I don't know alot about IRA and would love to learn more from people who do research.