If you're talking about giving legal power to websites' ToS to define what software may parse the data you download from their servers before/after rendering it to you, you're opening a gigantic can of worms, and I don't think most users would be particularly happy with that.
Seems reasonable to me that the adblocker should act responsibly and block entire sites where the TOS prohibits its use.
Not hard for sites to set something in robots.txt to say "no adblockers allowed"
This is not true in any country at the moment as far as I know. There's some initial stupidness in the US like https://www.washingtonpost.com/news/volokh-conspiracy/wp/201... , but in practice that's going to be disputed in courts many times before they agree on some final version.
Especially since there's a related recent ruling (can't find the article now) which basically said - if your ToS are too complex and people are unlikely to understand all the details, they're not bound by it.