> WHY javascript code is even allowed to see all these actions of the user? We already loaded the page and rendered it

Nope we haven’t. At least not in a web application. At least not since the days Infinite Scrolling was invented. IIRC Twitter, for eg, only renders a partial list depending on the scroll position.

I once wrote a NER tagger, where implementing custom text selection allowed users to not stress about selecting the exact word boundaries when manually tagging 1000s of words per day.

I can probably find legitimate use cases for almost of these things in the list. While I agree with the broader theme of the article, this idea that the user agent should be a dumb display is not valid.