People often fear what they don't understand...
Although I think this is very valid I'd take a slightly different slant on it and add that:
As they don't understand it
, they can't really fear it
. They have a feeling of loss of control or an underlying feeling of uncertainty. From a negative mindset the uncertainty turns into fear, on the other hand from a positive mindset fear turns into courage. Small children are a good case in point. Go onto any children's ward and you will find an enormous number of truly brave and courageous souls. Somewhere along the way many of us lose our awe and wonderment of life.
I think that perhaps power is the wrong word to use from a spiritual perspective.
The crux of the issue for me is:
What is the motivating factor in the search for power?
What are you going to do with it once you get it?
(and what is it going to do to you)
It is easy to get wrapped up inside our own worlds and forget the bigger picture.
I think it is fairly self explanatory why spirituality is closely linked to many Martial Arts. At a basic level you cannot go around teaching dangerous techniques to any tom, dick and harry. More importantly I think it is the framework that they are taught under that defines how the information will be taken. There are alot of people that just should not be trusted with 'power'. For a person to rise to the top of a major corporation or become a senior politician, there has to be a strong base desire, a motivation, if this is based on an egocentric perspective then things surely deteriorate for the others around them.
Selfless altruistic characters are an unusually rare bread and don't generally have the kind of desire needed to rise into a position of 'power', obviously there are some wonderful exceptions.
Maybe a better tranlation for 'spiritual power' is 'strong positive spiritual energy'.