A frequent refrain among immigration enthusiasts is "But we've always been a land of immigrants, and we used to discriminate against the Irish, but now they're normal and mainstream! Thus immigration works!"
Except that, if you look at the history of the USA, Irish immigration has been an unbridled downfall:
By the 21st century, an estimated 80 million people worldwide claimed some Irish descent; among them are 50 million Americans who claim "Irish" as their primary ethnicity. - Wiki
The history of the Irish in the USA has been one of supporting maniacal religious movements, liberal politics, local corruption and the growth of huge cities. In short, they imported the same failings that made Ireland an impoverished rock with dead potato plants on it, and brought them into American life.
Whoever decided this was a good idea probably did it for the same reason we're importing hordes of Mexicans, Vietnamese, Guatemalans, etc.: cheap labor and even cheaper voters. Expect each group to re-create what it had at home, with the same disadvantages.