but an mp3 can be good quality but is nowhere near identical so what is the big deal.

Because once the MP3 has been made, it does not lose quality on successive generational copies. If the first rip is done well, then it is very close to identical and can create an infinite number of identical generational copies.

For that matter, one could rip to a WAV or FLAC and then have zero degradation, and I'm sure the RIAA would be equally unhappy about that. MP3 happens to be the popular format now so it's the one they're concerned about the most.