You've come across the single factor that is most influential in endangering the Irish language - the fact that it's treated by many people as a contest, not a communication.

Perhaps what you should do is introduce any song in Irish (or Gaedhlig) with the proviso that you're not singing in your native language, but out of love for the song.

But please do keep singing our songs. They need to be sung to live.

(Incidentally, there's a scene in the book Bel Canto by Anne Patchett - a brilliant book - where a character is raving about an opera singer's superb phrasing in, I think, Italian: how perfect each word is, how distinct and pure. Another character, an interpreter, thinks to himself that while every word is perfect, few native speakers would understand the singer, because she is completely un-fluent. But not un-beautiful in her singing!)