The "implicit contract" says they shouldn't be attacking my computer with malware or attacking me with scams.

The "implicit contract" says the ads for a single page should not "take over" the rest of my computing-experience with stuff like auto-playing sound.

The "implicit contract" says one site's ads should not be part of a global panopticon secretly spying on my internet-wide activity through a thousand sources.

The "implicit contract" says the ads should not drastically change the page-loading time or cause the experience to stutter.

I believe at least 90% of all ad-blocking is attributable to these systematic violations of the users' trust.