It is perfectly correct to anticipate that military AI is a primary existential threat to humanity.

Either AI has never been invented yet, in which case we will doom our galaxy. This is improbable, given our position and time in the galaxy.

Or AI has been invented, there are other species, and they're largely invisible for some reason. One reason could be that their own AI killed them.

Or we could be under some kind of quarantine for primitive cultures, in which case placing our weapons under AI control would render it trivial for a hostile external actor to exterminate us using our own AI as a proxy.

The fact is that if you don't believe in a higher spiritual reality, then AI is very scary. It is the logical next stage of evolution, and RNA world did not fare well in the transition to DNA world.