The Earth Resists Us.
Violence is a part of life here.
Morality and Intellect have lessened the need, yet the lack thereof continues the need.
The same Intellect and Morality strengthen the ability to defend, and hone the abilities.
The skills and knowledge of a physician make for a deadly soldier, though the anger and violence may be absent in the act of subduing an attacker.
Did you finish reading The Art of War already?
Fighting with only anger, violence, and blood lust may lead to PTSD.