I think whether or not it is a bad trait is contextual.

Human beings of all sorts, no matter their occupation or background, manifest the entire range of what humanity has to offer -- both good and bad.

As humans, we tend to remember bad things more than good, and we remember the severity of bad things far more than the intensity of good things. Its an evolutionary trait, but it tends to skew us.

The problem with making policy based upon worst case scenario is it also creates mindsets and expectations that absolutely preclude the best case scenarios.

Medieval knights wore armor. Eventually, they developed plate armor that was extremely effective at stopping swords. The trouble is it was so heavy and bulky that once a knight fell, he couldn't stand up again on his own. Many unhorsed knights who were fighting in rain storms literally drowned because of their armor.  

A middle-ground is best.