Forget the particulars for just a moment. Forget arguments about the probability of the existential risk, whatever your personal assessment of that risk is.
Can we agree that people should not be able to unilaterally take existential risks with the future of humanity without the consent of humanity, based solely on their unilateral assessment of those risks?
Because lately it seems like people can't even agree on that much, or worse, won't even answer the question without dodging it and playing games of rhetoric.
If we can agree on that, then the argument comes down to: how do we fairly evaluate an existential risk, taking it seriously, and determine at what point an existential risk becomes sufficient that people can no longer take unilateral actions that incur that risk?
You can absolutely argue that you think the existential risk is unlikely. That's an argument that's reasonable to have. But for the time when that argument is active and ongoing, even assuming you only agree that it's a possibility rather than a probability, are we as a species in fact capable of handling even a potential existential risk like this by some kind of consensus, rather than a free-for-all? Because right now the answer is looking a lot like "no".