What will prevent them from literally unplugging it from the wall?
It will control the electrical grids with 'smart' decisions that improve the efficiency and make it's removal impossible without taking out all power.
It will integrate with water and waste processing to ensure leaks don't exist in the system and everything is working smoothly.
It will be in all transportation and distribution networks because companies want profits from efficiency before they'll think deeply about the risks.
Then after it's pretty much everywhere ensuring you down starve and dehydrate, who the hell would be dumb enough to unplug it in the first place.
It's kinda like telling people to shut off every computer today, not a chance in hell it would or could happen without terrible life risking consequences.
And yes, that's certainly a plausible hurdle.
Can't unplug from banking, even when literally communists (literally literally, I've met some proud of being communists, they still got a mortgage).
Coal and petroleum-based fuels are slowly getting unplugged, but the issues were known over a century ago, and the transition only became relevant scale when the alternative was already much cheaper — and it's not yet clear how much damage has been done in the intervening years.
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Any AI worth using is so because it's at least one of [cheaper, better] than a human on the same task: any AI which is both more expensive and worse just doesn't have any reason to be used in the first place.
This means that "unplugging" an AI comes with a cost of losing every advantage that made you start using it in the first place.
An AI which is "only" as misaligned as one of the major industrial sectors of the world, that is made out of humans who are necessarily able to care about human interests, and which drove a huge amount of economic improvement and brought with it derivatives such as basically all polymers, is still capable of great harm. And because of those benefits, society as a whole still has not unplugged the oil drills.
The more power there is in a system, the harder it is to keep it aligned with our best interests, even when there are humans not just at the wheel but occupying every step.
And the more aligned it is, the harder it is to "just unplug it" when things — as is inevitable because nothing is perfect — do go wrong.