Clearly noted (now!) re, in '50s: strong presumption that Techno implicitly could solve any problem ('you could parse in Boolean?' they may have meant; the smarter ones, anyway.)
My 'institute' was certainly rife with such bubbly optimism.

But for those not up to Drake's eqn., Sagan's audience: I thought he did a decent task of conflating such missing-parts? into that ominous phrase about
(Our!) tendencies to commit seppuku in the name of any number of cockamamie rationales.

(As with 'I.Q.' too..) I doubt that any number in an equation could capture such a species-wide defect, into some Probability #.
Besides if that blindness tracks "IQ", we're certainly doomed to a death of un-Natural kind, anyway.