Just because the author can't think of a way to cause mass death with an engineered virus, doesn't mean an AI won't be able to think of one. (There are several biological threats the author hasn't considered. I'll just leave it at that.)
The author can't think of what a superintelligence will do, because they are not a superintelligence. But that is not really what people are concerned about, so I think the objections here are quite meaningful. If there is a fully general superintelligence - in the current state of alignment - we will all die for some reason. It doesn't really matter what the reason is.
is this a tautology?