This is somewhat of a weak spot, in my mind... 

Consider a contraversial update to Bitcoin Core, about which many node runners are on the fence, with respect to upgrading...

All it would take would be for a fake-news headline, claiming there to be a vulnerability (that didn't actually exist), and a large swath of on-the-fence users would panic-upgrade, to the contraversial latest release.... 

 Could be. On the other side: Of the update is really so controversial, then there would also be a lot of other people who were against this update. And then there would probably also be some people who have the means and abilities to fork a Bitcoin version without that update.