It´s not evil to join the military because it is noble to defend yourself and your poeple within your borders. And being effective at it is also not evil. This is so you can be fearful so you never need to utilize what you have learned. In Norway all of the military branches are under the umbrella name "The Defense".

Like most traditions within Martial Arts, you always start with a bow, then a block and then a counter-strike, usually met with the same ferocity or lethal force as it is presented to you.

So military becomes evil once it starts attacking! Especially if it moves out of its own border, no matter what justification it uses... It shall NOT ATTACK.

Psychologically I believe every soldier can justify killing while defending themselves and their people on their land. I believe they will sleep well at night compared to the attacking soldiers who invade and kill others in their own land.

(The Norwegian military has lost face since it joined in Afghanistan and bombed Libya. It was NEVER designed to be part of such attacking. The pilots themselves have been interviewed and said it was without proper orders most of the missions. They should just bomb if they saw something suspicious on the ground. It went from "The Defense" to become "The Attack".)

As a side note - in Ancient Rome the soldiers spent 90% of their service time building infrastructure and buildings for the common good. Something to think about.