Fear is very, very fast and almost never fails. It allows the danger to command your attention in a way logic alone can never achieve. It also stimulates the whole fight-or-flight response, souping you up with chemicals in case you need 'em. It has it's limitations, but on the whole it does a much better job than logic would alone IMHO.

Being geekish myself, I totally understand the desire to replace everything with cool, calculating logic, but our basic instincts usually do a pretty damn good job. An easy example is if you put your hand on a hot stove, you will instinctively pull away, often even before you feel pain or heat. If you relied on logic (gee, this stove is hot and my hand hurts! I should pull my hand away) your burn would be much, much worse.