But Facebook, like most social media platforms, is addictive, so it is not obvious that in the long term a reasonable usage of them will emerge.

Lack of movement in sales after paying Facebook for advertisements will emerge, and that will certainly be noticed.

You may overestimate the sophistication of ad buyers, and underestimate the ability of Facebook to convince buyers that their ads are working

The increased ability to track the efficacy of ads is the value of the tracking that the internet enabled, hence the value of Facebook. Hampering this ability to match ads to purchases reduces the price these ads can be sold at, it is what the whole article and situation are talking about.

Movies make billions of dollars from users who don't contribute any content. As long as users consume content, who cares who makes it?