Social pressure, social conformity is a strong driver.
If I learned anything during my four years of studying general psychology, is that we as humans have much less control over our decisions than we think we do, especially when it comes to the first few seconds after a stressful situation.
I would defer to your broader knowledge. Wouldn't it go down like this. The body receives a blow and the ear is sending a massive signal that the body is upset. The interneurons send an emergency signal down to the adrenal gland to prepare for emergency action. The adrenal glands respond with a flood of epinephrine to flood the system with glucose from the liver, jump the heart rate, expand the airways, and constrict all blood vessels incase of injury. The rush of the autonomic nervous system kicks into high gear and is already calculating out motor response in how to take down the attacker. The motor neurons are rehearsing various scenarios and as the eyes sweep across Kolstad, the autonomic nervous system calculates that a kick to the head is the best course of action. Nelson is still not consciously thinking about poor, poor Kolstad on the ground, which is about 0.3 seconds away from coming into focus. The kick is away, the attempt at moral reasoning is coming into focus, the blow lands and suddenly regret appears in the mind as the confusion between the automatic system comes into conflict with all the lessons of Sunday school and mom and dad telling Phil to not get into fights over frivolous matters. So, he withdraws from the immediate vicinity and is wrestling to regain control after the flood of bodily response to the attack. He looks into the face of his friend who is pleading with him to not do anything else. Nelson looks over at the fallen Kolstad and a lifetime of fear now overwhelms him.
And yet, the law of the land states that he should be a good boy and retreat, ignoring all science on the subject of a dual track mind and how primitive survival mechanisms can make clear headed reasonable thinking a blackout moment. No, beer didn't do this to Phil Nelson. Millions of years of survival school and selective trait acquisition successfully led him to do what our ancestral genetic code told him to do. Kick first, ask questions later.
All in all, we will construct a legal theory of his guilt that ignores any scientific explanation of what happened in those brief seconds and we will tell ourselves that because Kolstad received terrible injuries to his mind that Phil Nelson should be held in prison to waste away even though we all know that Phil has already learned the terrible lesson not to hang out at bars late at night with your girl friend and that more calm social settings may be more suitable for a long and happy life.
I guarantee to everyone that Phil Nelson is not a social threat to humanity. Not then. Not now. Simply because we hire idiot legislators, drug addled Governors, and ego maniacal lawyers to prosecute for the perceived harms in our lives, doesn't make all of this okay to waste all these lives for some emotional pabulum. What Nelson and Kolstad need is some reconciliation and responsibility taken by both sides. Phil may have to own up to some economic damages for years to come. Kolstad needs to work on rehabilitation and to also stay away from the bar scene.
The bottom line suggests there is no justice that can possibly restore both men to being whole again. Kolstad may battle the injury for a lifetime. Nelson will have his superlative reputation taken away as so many have adopted him as an evil monster totally out of control. What good do these ideas of justice have for any of us? Drop the stones from your hands folks. Lend a helping hand to these people. They need our support.