This is one of those topics that many find hard to understand. It's also one of those topics that ANY who are considering joining the CF and those who are members of the CF should seriously consider.
Society in general tells us throughout our entire upbringing that is is abhorrent to kill or to cause harm to others. Get into a fight in the playground, and you are told that that is wrong. You should turn the other cheek. Killing is bad. Many religions state that if you kill, you may very well end up in hell.
Most people who join the military do not do so with the expectation or desire that they will have to kill someone.
But those who serve need to put a lot of those moral issues and upbringing to the side once they join. You see this from the first time you fire your weapon, at a target shaped to simulate a charging enemy soldier.
As a member of the military, you need to be aware that in a conflict, any action you take, duty you perform, or order you give may very well, either directly or indirectly, cause the grievous harm or death of another human being. Wether you are the infantryman with the enemy in your sights, or the vehicle tech who fixed the vehicle that carried the soldiers to a TIC, or the clerk who pays the members, you have played a hand in the action.
While you may go your entire career without first-hand dealing of said situation, you are a part of a large organisation that is prepared to kill.
This isn't done for the sake of just killing. As mentioned, there is a time and a place for any sort of action. But we must be prepared to take that action, and to take that action at a moment's notice, without having any ingrained moral issues causing hesitation, as that may come at a cost of more lives.
If an individual is unable to come to terms with this due to their moral beliefs, they should not join, or stay in the military. There are many different ways to honourably serve ones country and people without actual military service.
But if you cannot, in good conscience, perform acts that may be required of you in the military, you should not be IN the military. Not trying to be callous here, just realistic.