Cartel members always have incentives to cheat - if one site can become popular by not ad-walling like 90% of them do and regurgitate the content of 90% they will do it and disregard "the big picture" especially considering the low barriers to entry. They have no enforcement mechanism to keep everyone honest - the only way this sort of thing works is if you "outlaw" non-ad-walled sites - something like google not listing those sites - otherwise not happening.

A restaurant cannot beat other restaurants by making its meal free to all.

No, but it can by offering better service, better food, better decor etc.

But customer needs to pay

Someone needs to pay in a society where a restaurant owner needs money to eat. But that someone doesn't have to be the customer, doesn't have to be every customer - and the economy might not be structured to require anyone to pay for things, in which case both the restaurant and the customers get everything without money. (Why would people work there? Maybe vocation or hospitality, maybe they wouldn't and robots would instead.)

Oh, good dreams...

I would say just the reverse, this will work more and more.

Under what scenario?