So many

Full warning, I like that movie.

I don't think it celebrates abuse so much as it does point to the nature of abuse and self abuse between artists and their art, both from those that hold the keys to the kingdom of your success and from within as you bend yourself to meet those needs entirely of your own free choosing and obsession.

The protagonist gets everything going for him. His family does love him, but can't connect with his musical obsession even though they're proud of him. He meets a girl he really likes, wants to get serious about, but to do that would mean to choose between her and his obsession. J. K. Simmons character has churned out success by holding himself, and by extension his band, to an extreme standard that requires that obsession to keep up with. He sees the potential in the protagonist, pushes him to reach those heights but also demands in very plain language that he be subservient to the craft. And every time the movie makes it clear that the protagonist is given a choice between regular, healthy life and the rigors imposed by his dedication, he chooses art every time.

The reason I don't think it celebrates abuse is because he isn't 'winning' at the end of the story. He's doggedly pursuing his dream and giving his all to the band, the music. He's sweating profusely, his relationship with his parents is estranged, the girl of his dreams left him, and he's just told his idol of an instructor that he'll cue the instructor in and with that he gives in and gives the ultimate solo. It cost him everything, but it did pay into incredible music and the culmination of his efforts. Give it your all and you can have what you sought but if you give it your all and you'll have nothing left.

Only if you think the ending is a good one for Neman. I think it's a bad ending, where he gives in fully to self-abuse and abandons his crush, and even his dad to some extent, so he can keep forcing himself to try and be #1. The message, to me, is that it's a stupid way to live and totally not worth it.