As someone who always thought there was something mightily hot about how step dancers didn't move their arms as their legs and feet did, yeah, right. I'd like to know how that didn't take in other countries no less Catholic than Ireland where they move their arms all over the place. Going to look for evidence of a religious ban on dancers moving their arms I read that it's just one of a number of speculations for why the custom is as it is, one that looks pretty improbable, to me. Considering what else was going on as they were dancing, drinking and all of the other associated activities, why would that one be the one prohibition that stuck? I think the speculation that it was under the influence of 18th century dancing masters who wanted to emphasize upright posture is more likely. After that it probably just continued as a distinctive custom and part of national identity. Or maybe people found it hot. A mixture of firm self-discipline and what looks like wild abandon all at once.
If you really wanted to get into a bawl, Colin Dunne was many times the dancer that Michael Flatley was. But I'd never want to have the knees and hips you get from dancing in heel shoes after a few years. Glad I didn't take it up when I could have.