It is not, because we should not expect a manufactured technology to behave exactly as an evolved one. My understanding is there is not much incentive for a virus to kill off all its hosts. When they do it is largely an accident, and it is not uncommon for a severe virus to eventually get replaced by a less virulent and thus more successful strain. It's pretty hard to hill-climb evolution to such a point since the virus could starve itself in the process. And induction on evolution feels misguided to me. Consider our species. A million years ago it would have seemed completely reasonable to state that the absence of advanced tool use in the kingdom of life suggests it is biologically impossible. After all, such a thing had not occurred in hundreds of millions of years!

To be clear, I am not saying that such a virus will exist eventually. I am just noting that the arguments displayed here are not completely tight, and there are unknown unknowns at play. Some things are unfalsifiable. This is common.