One of the more profound (and abused) scriptures is the one in which Jesus tells people to love their enemies.
One aspect of that teachings is that Jesus recognized that there was a significant difference between enemies and friends. After all, in order to obey his injunction, one first has to recognize that a person is in fact one's enemy.
King David didn't have any trouble telling the difference between a friend and an enemy, which is a good thing, since his first official act of obedience to God was to slay Goliath.
Jesus knew the dark hearts of men far too well to trust them or to fail to understand that there were many human beings who would be all too happy to kill him.
The point I am trying to make is that loving one's enemies is not tantamount to being naive about the fact that they are one's enemies. You can tell an enemy from a friend by examining that person's manner of treating one. Friendship is not free of obligations. There are things one cannot do to another person if one expects to be regarded as a friend and not an enemy. I could list those things specifically by name, but the bottom line is that they call it The Golden Rule for very good reason. They do not call it the Golden Suggestion. Obeying it is not optional in God's book.
A lot of Christians claim that they understand and follow the Golden Rule, but all you have to do to know they are sometimes lying is to ask, "Do you really mean to say that you expect me to believe you would want someone to treat you the way you just treated so-and-so?"
People who endorsed slavery from the pulpit, during the antebellum era, presumably claimed to practice the Golden Rule. How curious. I can't imagine any of those folks volunteering to be anyone's slave. Slavery is only one of many possible examples of believers who lack or lacked the integrity to obey the Golden Rule.
The Golden Rule does not preclude punishing those who have deliberately done things to deserve punishment. But even wrongdoers believe in the principle of reciprocity, if one closely examines what they claim to believe.
So act with integrity, and always keep the Golden Rule in mind when deciding how to treat the people. You will be judged accordingly.