

This points to a flaw in your question.
You probably should have said “foolproof countermeasure” if you really just wanted to remove nukes as a factor to see what happens.
But you said “foolproof deterrent” and now you’re quibbling at people over whether a psychological deterrent can actually be foolproof.
Maybe not, but then your question is nonsensical. The fact is that we are already using guaranteed total destruction of the world as a deterrent and it has so far worked. What more deterrence are you even suggesting we might add to that???
They probably don’t believe you because most of the time a 20% growth rate doesn’t just stay constant for a decade, allowing for such simplistic extrapolations. There are examples to the contrary. But a 20% growth rate means 750% growth over 10 years and that is a lot.