[mars]

The reason "there was no realistic defense against low level Ju 88 oe Me 410 attacks." was that no such scale of night attack occurred before, Luftwaffe could not expect to be so lucky next time.
Luftwaffe could not go after US airbase in UK in the daylight, that would be almost equal to commit suicide. In the night, the limitation of the navigation technology alone would prevent them from finding their target, besides, many US airbases for heavy bombers units located beyond the range of the German medium bombers anyway. And even they found the airport, what the chance their bombs could hit the target? From the experience from RAF, we all know the accuracy of the night time bombing was notoriously low. At last, let us do not forget the fact that RAF night air defense system was among the best in the WWII airforces