> certain number of free riders

This implies that ads means paying/sutaining for the service, and no ads means not paying/sustaining.

This hasn't been the case for a long long time. Even paying customers get ads piled on them. Sure for many sites ads is the whole business. But there are also many business that

1. Never had a business plan to begin with, even the ads won't sustain them. The goal is just to be bought by a bigger company or become a loss leader and then "figure it out later".

2. The goal is to maximize profits by any means necessary even with paying customers upon which a sustainable business could be built. But instead we get dark patterns, abuse of user data and ads.