I agree that fear is a necessary feeling in life, a great trigger; it's something physiological, mainly due to the adrenaline released.
The point is that fear can be a good motivator only if you have the right mindset, if you know yourself and how to overcome it. I know very capable people with the right attitude who have been frozen by fear in key moments
Yeah, it can certainly cause a person to become immobilised and ineffective in action and thought. That's not a good use of fear though. Of course, everyone is different and fear itself can be many different things each of which cause different reactions.