The bomber will always get through

And yet, things didn't turn out that way.

No? It's true that we don't have literal bombers devastating cities, as Douhet and Harris envisioned; but the nuclear-tipped ICBM occupies the same strategic role. It seems to me that Baldwin was correct about the strategic principle, that there is no defense except retaliation, and wrong only about the implementation and timescale. For that matter, if you used atomic bombs, even literal bombers would be quite sufficient; ten percent was considered heavy casualties in a WWII raid, but would presumably have been acceptable if the enemy really lost a city in exchange. With nuclear bombs you could achieve that - the problem wasn't so much the defenses, it was that the throw weight wasn't high enough. The bomber did always get through; it just didn't do as much damage as people thought. That was a problem with bomb technology, not with the strategic conception.

It's also worth noting that Douhet envisioned a mix of high explosive, incendiary, and chemical bombardment. Clearly this would have given even 1940 bombers a much higher effective throw weight, and both sides contemplated the use of gas, and took precautions - witness the amount of gas masks handed out in London during the Blitz. Why didn't they use it? Because they were afraid of retaliation in kind!

In the bomber analogy, it seems to me that friction is an argument for increasing our timescale and perhaps looking to unexpected implementations; it does not obviously decrease the overall probability.