It's very simple. Google has concerns of click/impression fraud. Unattested traffic would be more likely to be fraudulent. Not paying for unattested impressions/clicks is therefore an easy way to cut costs and combat fraud.
Now if Google cares about real impressions it's still terrible no good very bad evil.
It's good for google to care, it's not good for them to do this.
I don't think Google has actually done anything. The bar for experimenting with new code in Chromium is pretty low. This Chicken Little reaction to a non-starter is just a result of developing in the open.
But you can "care" about something in good and bad ways, and the criticism is not "Google bad".