That's an agreement that's made by the participant though. I support fan efforts generally speaking to expand the reach of whatever artistic interest they have, but if someone is making money off it that changes things. If I was a photographer, and someone was using my photography without my permission and not paying me ostensibly because their free advertising is sufficient to pay my bills, I'd be pretty pissed. That said, my only argument is for their hypothetical right to be pissed, not necessarily that they should or are.

I'd be even more pissed if someone made money off my work and subsequently made that argument, refusing to pay me because I should be grateful for the exposure.