One of my Sempai is an old Karate man. He once explained this flowing into the lethal response as to why he's training in Aikido. He knows he can kill unconsciously and has been training to rewire his lethal responses.
In the crunch you respond automatically ; if you have trained lethally that's what will come out. I believe the practice of Aikido waza will lead you to hardwire other responses which will end up with no one dead.
In the crunch you don't have time to think and decide.