[emberrider]

Because defending themselves would necessarily require acquiring their own nuclear deterrent, and the US correctly realized that a world where every country had nukes was a world where they'd eventually be used. Alliances like NATO reduced the risk of human extinction while pulling countries closer into the US orbit. It's ridiculous to look at that from an ROI perspective; the ROI is not dying in a nuclear war.

[remarkEon]

I think you need to reevaluate your understanding of Cold War history if the argument you're making is "we started NATO to reduce the proliferation of nuclear weapons".