> I don't follow why you are so opposed to the visibility api.

It's in the second sentence.

  The ability for a website to see when you click on things outside of the page itself (either by changing active window or tab) is quite unexpected from an end-user perspective

> what sort of stuff? And how is it related to the visibility api?

It's in the linked article. At least a few of those events are implemented with the visibility api.