This is a very interesting thread. At the risk of bringing fire down upon my poor little gray (or grey, as it were) head, let me speak in defense of all those non-Irish Irish songs, regardless of what we think of them, their origin, or the categorization of such...
Many of them were, of course, of Tin Pan Alley and dance hall origins. Yes, they were written to exploit sentiment, stereotpyes, bigotry and anything else that would make a dime. Many of them were truly awful, and died natural and unlamented deaths. Others endured through merit--musical, literary, or emotional--and because of real or fictitious beliefs about them. But here are a couple of thoughts.
1. Many of the Irish immigrants in America were maintaining traditional music, in their lives, but not making any money at it. So, some of them wrote music for publication and performance in dance halls and taverns, which enabled them to live long enough to preserve genuine ITM in this country. Eventually, interest in true Irish music arose, and lo, here were the people with the memory and the music, ready to pass it all on.
2. Many of us--alas, I must count my sullied soul here--were brought to a genuine love for "real" Irish songs and music through the back door of pseudo-Irish Tin Pan Alley stuff. In the quest to learn more about the music, I found out amazing things, heard beautiful and meaningful songs, and became more and more drawn into true Irish song. Does that diminish my value as a performer and lover and listener? Sure, lots of people think so, because they value the "pure drop" and worry about what is real and what isn't. That's how we get fascinating conversations like this.
Pax