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Adjusting for surviving birth, life expectancy varies wildly in both directions (although even considering that, "longer" is definitely less of a promise now than it has been for the last several decades).

I don't know if it's particularly optimistic - if you're (accurately) saying current life expectancy numbers don't take catastrophic risks into account, neither did calculations of life expectancy back then. Unless you think there is a higher risk of catastrophic events now than there was during the cold war.

Life expectancy has plateaued and may be trending down in the U.S. The culprit is likely obesity. (See https://time.com/5100737/obesity-lowering-life-expectancy-un... )

Let's say larger variance in life expectancy--we expect a longer tail of a new generation living longer.