Because I am pro-capitalism, I utterly disagree with your premise. In a real contract, parties can negotiate and come to a meeting of the minds. Here's how it actually works:

* A website serves me a page with a place to put ads on it.

* I reject their offer to serve me ads.

* The site has the option of deciding not to serve me any more content, typically by showing me an anti-ad-blocker popup. If they continue to serve me, they've agreed to my proposed contract alterations.

* If they choose not to serve me, I can decide to accept their final offer (by disabling my ad-blocker) or reject it (by closing the tab).

What on earth makes you think that the negotiation ends with the initial offer? That's not how bargaining works. This isn't some Soviet-style take-it-or-leave-it scenario.