I once worked on a video game that was translated into many different languages for free by passionate community members. Since the game was frequently updated,

I once worked on a video game that was translated into many different languages for free by passionate community members. Since the game was frequently updated, eventually it made sense to give these "community translators" early access to new text. Also it made sense for them to provide their translations in a form our pipeline could consume. Voila, they have unpaid jobs. I skipped a bunch of steps there, but basically through no malicious intent on anyone's part, people's passion was leveraged into making them work jobs with expectations and deliverables. Of course they were free to not do the work, but they'd be letting their community down if they didn't. At that point we had an internal discussion about the ethics of the system, and wound up deciding we should pay them.