Remember there are off switches for human existence too, like whatever biological virus a super intelligence could engineer.

An off-switch for a self-improving AI isn't as trivial as you make it sound if it gets to anything like in those quotes, and even then you are assuming the human running it isn't malicious. We assume some level of sanity at least with the people in charge of nuclear weapons, but it isn't clear that AI will have the same large state actor barrier to entry or the same perception of mutually assured destruction if the actor were to use it against a rival.