The old warriors said, "Weapons are a necessary evil and Heaven detests them. Use them only when there is no other possibility." It is the nature of Heaven to give life and nourish all things, and any weapon used to kill, whether it is a sword, bow, or naginata, is in direct conflict with the will of Heaven. Since these are used to kill Heaven's beloved children, Heaven hates them.

We must also consider that weapons are instruments of Heaven's wrath and judgment. In the natural cycle of things, spring breezes bring life and greenery to the earth, but the winter frost destroys the life that the spring brings. Heaven's love and judgment follow this same path. It makes sense to put a stop to evil because human beings will take advantage of an opportunity to commit evil, and once that evil is revealed it must be judged. For this purpose, weapons are also approved by Heaven.

A single tyrant may kill or torture thousands of innocent people. If you can save the thousands from death or torture, is it not best to kill that one man? In this way, the sword of death is also the sword of life.

-- The Secret Teachings of Yagyu Munenori

look for a longer post on this topic later... because i think its an important one. possibly, one of the most important ones.