Pre-MAD MAD before WWII

http://www.littlegreenfootballs.com/weblog/?entry=4760#c0069

In the 1930's (pre-radar), it was assumed that the bomber would always get through. The situation was almost identical with the concept of MAD today - any attack would succeed, and cities would be erased by poison gas, incendiaries, and high-explosives.

How true is this?