Then paywalls and interstitial-ad-walls would pop up everywhere. It wouldn't be very technically hard to force users through an interstitial ad before they could get to content. Quickly people would realize the previous way sites did ads was actually better.
What will really happen in the scenario you outline is either users will stop using the site (as much or at all) because of the escalation in the ad arms race, and/or wait until ad-blocking software stops those kinds of ads, too.
I think users are more forgiving of advertising that obeys the social contract (they get something out of allowing a marketer to have some of their precious time and attention).