Don't forget: there are plenty of humans that would love to help AI agents cause chaos, many of which would do so merely for the "lols," but also adversary governments, terrorist organizations, etc., would definitely appreciate the opportunity to support a rogue AI to cause whatever problems it can.

So it's not just the risk of an AI managing to do this by itself (which is pretty risky in itself), but also the risk of good ol' fashioned human actions.