For a radio-type service, I don't think anyone should be able to negotiate higher rates. I think there should be mandatory licensing.
For negotiating a lower rate... I wouldn't try to make it illegal, but I still don't like it. I have no particular reason to think it will be an upstart or an entity that you could say 'deserves' more attention. And taking less money for more exposure doesn't sound like something I want to encourage.
What if I want to give it away for free? How does that fit in your authoritarian distribution system?
If you want to give your music away to people, that's great. This is just about the price to Spotify and services like it.
If you don't want the royalties from Spotify, you can do something like donate them to charity.
Giving Spotify a discount is something I'm not fond of, because you're either hoping they give you better placement which is basically payola, or you're getting nothing back so you're making a donation to a giant corporation.