This is a good question. I believe you need to inject an element of fear into any martial practice. As an Aikidoka progresses he/she must at some point be confronted with atemis that are aimed to hit every time, otherwise a false sense of ability inevitabilty will follow. Even then as we all know this still isn't the same as a street confrontation with the (as a rule) swearing and aggressive body language. Its that that causes the fear/adrenaline to hit the body. The building of a strong spirit and mind through constant hard training will help the individual deal with fear but never free them from it. Having a degree of exposure to an element of fear in training now and again will at least give the practitioner an idea of his/her bodies reaction in a confrontational situation.
All the best