I thought all Irish girls were named Maggie.

Aine,
I understand your opinion in the context of your experience. As one many generations removed from potato blight immigration, I see things differently.
The reason Irish Americans don't rise in anger towards Notre Dame's "Fighting Irish" leprechaun, for example, is a matter of approval. While most Irish Americans have some sense of being that, it is also integrated with being white Americans. The use of such icons should never be in spite of some minority objections, but can be with their approval, generally speaking. We're not in the minority anymore anyway. We can poke fun at crusty stereotypes because they're now obviously untrue.

Having read Uris' Trinity three times over the years (as the title suggests and American Irish-ness should require), I have felt the Irish experience in 3 ways. First reading, at 14 years old, taught me the history of the troubles and value of a great story.
At 20, and during the then still ongoing struggle, I felt the anger one is more open to in those years of piss and vinegar.
Some years later, a reading with satisfaction in accomplishment for the struggle and that country I'm bound to by blood and name, even if those links leave me short of native knowledge.

So, I see Saint Patrick's Day as a symbol of accomplishment. What other hyphenated-American group has such a grand day?
Here, we not only wear the green, we drink it and, if you're in Chicago and inclined, you may swim in the green.

I like to think of the American celebration as symbolic of all Irish -- both of country and linage -- taking a big, green and satisfying piss on Queen Victoria's grave.