If ad-supported sites would return an optional response header indicating such, and their opinion on adblocking visitors. E.g.:

  Advertisement-Permission: [required|requested]

And my adblockers had a config option to abort pageloads with an appropriate error message, if `required` or `requested`, then I would use it happily.

In the meantime, I'm browsing every site with all content blockers set at maximum, because any other choice is incomprehensible on the modern web.

If I consequently visit some sites that want me to consume advertising of which I am unaware, then that is entirely their issue, not mine.