Well we've both given one example: passionate users who believe in and want to support the platform.

Another example would be the business itself through the data they exploit. In fact, if they're collecting and exploiting user data, thus generating a profit from the user, then really they should be paying the user for the data.

You can't sell a car without paying for the nuts and bolts, yet data companies don't pay us for the materials we provide that are integral to their product.

There's certainly some grey area with a free service that collects data for free. I'd still argue this is wrong, just because the value exchange is completely disproportionate. But when you're paying for the product/service and they still collect your data (looking at you, Microsoft), then that's just really scummy and wrong. With the reddit API charges, reddit is asking users to pay reddit so they can give reddit data that reddit can profit from. That's fucked up.