Is Killing Always Morally Wrong?

To kill a person is the ultimate evil one man can cause to another, because it is not reversible and, in fact, brings the existence of a man as we know him to an end. Can such act be ever justified?

There are different opinions in what concerns this issue. Some think that killing people is inconsistent with the status of human. Some say that it is alright in any circumstances when it may be useful. Between these two extremes there is a whole philosophy of opinions, tinges of opinions, schools of thought and ideologies.
But what if we look at the question from the point of view of logic?

How the evil is supposed to be stopped if we let the one who causes it go freely and continue doing it? If somebody tries to kill you, doesn’t it mean that he has already stepped away from this “status of human”? In my opinion, once a person initiates violence for any reason, he rejects the protection the human moral norms grant him. Nothing should stop anyone else from retaliating in a manner necessary to protect oneself, one’s friends and relatives, one’s property or, in fact, any person and any property.

But it, however, doesn’t mean that…