Here's where I get confused by this economic justice:

I have a little personal project and there's a piece of it that could be hired out on mechanical turk.

The project isn't worth much much money to me, it really is just a point of personal interest. And the little task is interesting enough that a few people might actually do it for free.

So I could ask for volunteers. Worse things have happened: how many times do people fill out surveys completely for free?

Surely no one would say I'm exploiting anyone by allowing them to volunteer their time? After all, it's their free choice if they want to waste a few minutes on my silly project.

But apparently I would be exploiting them if I offered a modest sum as a small "thank you".

Why?