I think a hero who knows no fear is not a hero at all
A man with no fear is not fearless, he's just crazy. There's something wrong with him, and his life will be short. A hero with no real fear fears no right, as well as no wrong. He's dangerous, and sooner or later uncontrollable and twisted.
We always use fear in our games, and have for a long time. I'm not for mechanizing it up necessarily. As a general principle. And in most situations. But fear can both build gradually, as well as surprise and shock. You can also build up a slow stockpile of it over time, as well as overcome it gradually with practice, training, and effort. (Believe me, you get in dangerous situations over and over again you can still be afraid, but it doesn't effect you in the same way. Eventually, in some situations at least, fear changes from enemy to ally. Form the guy who is gonna ambush ya, to the guy who is there to keep you from getting ambushed.)
Therefore I also think it should be remembered that fear can be a fantastically good motivator, as well as an inhibitor.
Fear of very bad things happening to people you intend to protect can definitely motivate you in ways few other things can. What's bad at first gander, can also fire up the goose. Trash to treasure, and all that.