Disbelief
In WWII millions of Jews were killed because people just could not believe that such a thing could possibly happen. This tendancy towards disbelief is one of the most valuable human traits for those who would do such things again.
This is a video clip taken at an appearance by David Horowitz at UCSD. The important part happens at about 2:49 (the entire clip is only 3:28).
Disbelief contributed to the Holocaust in WWII, and even now people still do not believe that this is really out there.
It is.
What is worse, it is here.
