Thank you for food for thought.
I totally agree that the dojo is a controlled environment. However, peoples buttons do indeed get pushed in the dojo. I have seen MANY beginners who were quite frightened of even slow controlled blows or strikes coming at them in the dojo - not just among the more sheltered or previously traumatised women or young men who would freeze, flinch or retreat, but also young men who would react more aggressively than needed (the "fight" side of things) because of the fear.
Flip side, is that I believe one of the things we are training for, in learning to be relaxed under the contained threat within the dojo, is cultivating a response OTHER than "fight or flight" - since it is a sympathetic nervous system response, we can indeed work on active control of it - while some people are actually wired to not have it and to go into a more parasympathetic response (deep slow breathing, slower pulse) - and optimally our training would slowly be ramping up the pressure so that we learn to stay relaxed in more and more intense situations.
Breathing is important.....
At low kyu grade we emphasize gripping taking the partner into a technique, taking them down slowly and safely, this enables muscle memory into the correct ukemi. We start of with light but fast striking so people get used to the speed factor, not just from shomen / yokomen uchi, but from kicks punches, palm heel strikes, knee strikes, elbow strikes and so forth. It doesn't have to hurt or scare, but can develop the hard wiring to diffuse the "freeze" effect....