It's kind of a difficult argument without defining the terms.......when we say 'Fear'......are we referring to the intellectual acknowledgment of a threat? Or the resulting physiological adrenal response?
As to the adrenal response, that is the great debate in modern self defense........because it divides the fine motor skill technique set from the gross motor skill technique set.
Upon further reflection of the nature of physical 'fear', i.e. the adrenal response.....it seems more applicable the more primal the conflict, i.e. the adrenal response is very important to fighting using your physical weapons, you become stronger, more immune to pain and injury because of the adrenal state.
As we go up the scale of tools and conflict we find that the adrenal state tends to hinder effective actions on some levels......for example a highly adrenal state tends to hinder our ability to fire a weapon accurately.
Pushed even further to the high tech combatant, the adrenal state, beyond a lower optimal level of arousal, would be an impediment to a fighter, pilot, for example, attempting to operate his plane effectively in combat.
So, it seems that the more complex the task involved in the combat situation, the lower the optimal level of adrenal arousal.