I personally find it implausible, but some quite smart people have talked about it so I am also not dismissing it as pure fear-mongering.

The reasons I do not think it is plausible:

1. Limited real world projection: an exceptionally smart AI is less powerful than a dumb person with the capability of shutting off AI's power

2. Confinements: The AI 'escaping' incidents that got media attention were really the failure of infra, probably due to the scenarios being novel. But it is probably a lot better PR to say 'our model escaped' than 'our infra was poorly thought out'. A fully confined model has a significantly less blast radius (claude ruined this term)

3. The game theoretic aspect: 'If all else stays the same and AI kept getting powerful, scenario X will materialize' is tempting to think, but all else never stays the same. Especially with AI, there has already been enough fear and paranoia spread that people are unwilling to give an un-sandboxed AI control of a laptop, let along more consequential outcomes. And the already spread AI FUD almost guarantees that the outcomes where AI controls substantial parts of the infra/economy autonomously are very unlikely to materialize, at least in short/medium term.

I would love to hear competing hypotheses where an AI can cause something resembling extinction and how.