> it illustrates what Google intends to do (stop providing the service via an anti-adblocker script) if you do not follow their TOS.

Yes. They have complete discretion over what 'list of "things" and their URLs required to render a page' they decide to send any particular user agent (modulo copyright infringement, hate speech laws, etc.). There is no requirement that HTTP connections to 'youtube.com' should receive video data; or even HTML; or even that anything's listening on that port.

Cool story, illegal in my country. Also, the popup is blocked, so I don't even get to agree to it or not.

It doesn't matter what Google intends to do. Only what I do in response. TOS are not legally binding, they're a bunch of crap.

I wonder if the reverse would also work. If my browser's source code included a "TOS" that "by uploading content to and executing code on my machine you give me a permanent and irrevocable right to view/read the content using any software of my choosing" would that bind Google as well? Wouldn't that illustrate my intent in accessing Google's services just as a EULA I never get to read illustrates theirs?

Right. If they get to push a TOS on me, I get to push one on them.

I want Google to pay my rent for the next decade, and Sundar has to offer a naked lapdance at the Pink Poodle every time they send me an ad I did not explicitly request to be shown.

So if I can't read, but I watch YouTube videos, am I agreeing to a contract?

Contracts are only valid if signed.