Until the day where the main server serving the automated updates gets compromised and instead of serving, say, an updated Chrome, it serves a version of Chrome which a) is compromised on the behalf of a botnet master and b) never ever accepts any other update automatically.

Because people have been trained never to update their browser themselves anymore they'll think everything is fine.

Because hundreds of millions --if not billions-- of people are running Chrome suddenly you have the biggest botnet ever out there.

I find it very interesting that you fear extortion, exploits, DDoS, identity theft, invasion of privacy and whatnots as an argument for putting something in place which potentially can be way more destructive.

But of course this shall never happen right? Just as we haven't seen FaceBook getting penetrated and just as we've seen any major bank getting hacked right? And rogue employees also don't exist right?

Be careful about what you wish in the future...