Another take: It’s less about hidden fees and more about permanence.

If you created this service on a whim, what’s to stop you from taking it down on a whim as well? Accepting payment also serves as an establishment of trust in this regard, I wouldn’t just simplify it to “accepting money is bad”

I don’t mean to negatively criticize your service, I think it’s neat! You just might need to ask yourself some more questions like this to justify hosting people’s data