Now I'm thinking about this kind of scheme out in the real world. Some random points:
It's not like it's not there. Sometimes ad letters contain things. I've been given a kitchen knife for listening to a knife demonstration in a hardware store. Online we do get a lot of content and services even though it often doesn't feel like it is a good trade with all the tracking and security risks.
At the same time (maybe not online) it is a dark (grey?) pattern to guilt people into buying something. Or you might get junk you do not want in exchange for being annoyed.
And often you don't get anything but annoyed, as with billboards or leaflets.
So would it actually be more ethical to consistently give people payment for paying attention to ads? (I know there are some projects, yes.) Especially considering that now the ones profiting (minus costs) are not the ones who have to live with it. How ethical is a for-profit ad business where people are exposed to it whatever they do? (This is a question of freedom in my book too.) Then again, if I got a beer for every pitch I can't avoid I'd be black-out drunk at all times..
</offtopic>