1. If a musician doesn't want to have publishers taking a cut of the revenue from their music they are free to not have a publisher involved.
2. If a musician wants to distribute their music for free or have a pay what you want system they can.
If a musician chooses to use a publisher or big label then you should respect that; pretending that a publisher is a worthless middleman and using it to justify pirating media is laughable. If the publisher was worthless then the musician would not be using them, would they?
Do you really think people like Rihanna and One Direction wish they could set up a bandcamp account and get rid of the publishers? Of course not because publishers provide real tangible value.
Either respect the wishes of the musician by consuming through official channels or just pirate it, don't pretend you're a noble person by wanting to "donate" to the musician directly, if the musician wanted that they would not have a label involved.