I just personally find our infrastructure to be too damn fragile due to the reliance on technology. Imagine if all fuel pumps across the country were to go offline for a couple weeks. The results would be pretty catastrophic and you would see all hell break loose. We are so reliant on the system that losing any of our comforts would probably lead to all out chaos. It could be anything from cell phones, fuel, food, water supply, hell just shut down all the AC's across the country for a couple weeks and you'd see alot of people not survive. While I don't think AI is an immediate threat I wouldn't be surprised one bit if it were to result in the downfall of civilization.