Spotify, just like all other deliveries of the medium, are fine enough in their own vacuums. The problem comes with revenues and royalty splits between the labels and the artists/artists' management. 70% of all revenues Spotify makes goes to the right holders... which, 99% of the time, are record labels, not the artists (and that's the case whether in the mainstream, or indie). Now, let's say 70% of the money that the labels receive from Spotify goes into the labels pockets. You, the artist, are then left with 30%.
You think, "Fine, alright, I can live with 30%." Except that now, you have to pay your producers, engineers, background vocalists, featured artists, overhead studio costs, etc. Even worse, let's say you're a rapper. Now, you have a WHOLE ENTIRE ENTOURAGE to pay. That 30% quickly ends up being little more than 5% when it's all said and done.
And when you look at that 5% that you actually got to take home from your physical sales, downloads, radio spins, and streams combined, and you see the label you're signed to pocketing all the money you've worked your ass off to make for them, yet they keep coming to you trying to get into your other revenue streams, they want you to make cookie-cutter songs, getting between you and your art, threatening to shelve you if you don't make the Top 40... what part of this makes you go "THIS IS SPOTIFY'S FAULT!!!!"?