Free markets require the ability to appraise value. However the value of Nostr notes is impossible to objectively appraise, just like the value of friendship. When you start paying for these things, you are signalling that you don't care about the less tangible values and you undermine the interaction. That's why paying people to be your friend is not exactly a free market win. Just like paid shills, or people who only talk with you because you agree with them and stroke their ego.