I’ve studied this a lot but it’s been awhile. Drake et al we’re doing this during the Cold War and were definitely aware we could wipe ourselves out either with weapons or through ecological disaster. The L term is specifically about civilizations destroying themselves (although it can also be advances in technology which end radio-as-we-know-it).

The great filter is an attempt to explain the Fermi Paradox. Fermi was there, but the paradox necessarily came after the Drake equation.