The Catechism of the Catholic Church is not and never has been in conflict with Jesus' express and clear teaching on love, especially love of enemy. It may be in conflict with your interpretation thereof.

The Natural Law is not a dynamic. It is the rules built into the creation, one of which is Man.

Since the fundamental right of men is life, taking the actions to preserve it is consistent with the Natural Law. In fact, not taking actions to preserve your life, the life of your family, and the defense of your society may itself violate the  Natural Law depending on the conditions.

This is hardly a “peculiar position for the Catholic Church” since its uncompromising teaching against abortion is based on the divine command “You shall not commit murder”. That same command renders attacks on civilian population centers, such as the atomic bombing of Japan or the firebombing of Dresden during WWII intrinsically immoral.