The other question is what kind of effect ad based business models have on the economy and on startups. We all know that someone has to pay at some point. So ad based models are basically a way to shift that burden around to where it is most easily enforceable or acceptable for the consumer. Since startups are on average less able to enforce rules or gain consumer acceptance, they profit from ad based models more than others.

I believe to a large degree, the overuse of ad based business models is the result of not having an effective micro payment system. It doesn't make sense to buy a subscription to every single news site I'm consuming. It's just not practical. It's not even practical to explicitly agree to terms of service. Unfortunately micro payment systems suffer from a huge number of problems. Privacy being just one of them.