A man should kill if he so chooses. After all, it is how things have operated ever since the universe first began.
Simply because a person's heart wishes to dominate over others, they become king. A person becomes a saint merely because they have a strong desire to assist others.
A demon is created in that same moment for no other reason than his heart's desire to kill everyone.
To do what your heart wishes is the fundamental nature of everything.
But to become a king, one must make many sacrifices and engage in several conflicts, which also included hurting the monarch's subjects.
Because of this, people created a mechanism to keep against having another monarch rule over them.
The law, government, and regulations together refer to this system. The strongest element of contemporary society is that system.
It forbids certain actions and imposes restrictions, preventing you from following your heart's desire.