All the enthusiasm for ads only comes from the people who want to show/sell them. Not from the users who would be subjected to viewing them.
I think it's still a worthwhile discussion. Presumably the micropayments have fewer (or at least different) unintended consequences. And since in both cases (ads, micropayments) the side collecting the money is the one pushing them. So discounting micropayments solely on this basis isn't really a good way to discriminate.