As a former Google Play Music user and lover, it was the recommendations. I haven't found another service that shows me even a significant fraction of the music I like that Google did. I've switched to Spotify but it constantly recommends songs I've already heard or don't like and the shuffle feature gives me the same ~50 songs from a large playlist. It's something I've accepted but I miss the Google recommendations deeply.
It's not so much a rebuttal, but ask if they think stealing has any relation to depriving another person of something. Imo, they have a correct, though extremely narrow, definition of stealing that doesn't leave any nuance for comparing different kinds of stealing. Piracy, or as they would say 'stealing digital media' is not a kind of stealing that deprives another person of that thing, so clearly it's somewhat different than stealing money or physical property.
If they aren't willing to entertain that there are different kinds of stealing then they're ignorant of reality and it might not be worth your time to try to change their mind.
thank mr skeltal