Having zero cost to posting would make the recent tab full of spam over time… there should be some cost to posting things on Stacker News and making people filter through extra content.

However, I agree with your point about letting the free market decide. What if the free market chose the post/comment fee settings?

Over time, I think the way this could work is to enable anyone to create their own stacker news subs, where they can choose to set post/comment fees at whatever level they want, and then the free market of users will be able to decide which subs to participate on.