Self-defense = self love?

Currently I am reading After the Smoke Clears: The Just War Tradition and Post War Justice. The authors cite another book, Faith and Force" A Christian Debate about War, in which four historical stages in the development of just war thinking are laid out.  

The first stage that is given is the Christian thinkers Ambrose and Augustine

Augustine was a converted to Christianity after encountering Ambrose's preaching, so they are intertwined in their thought. According to the research in these two books, both of these men "instructed Christians to forego self-defense if attacked as a private citizen, for this would be an example of excessive self-love." (emphasis added)

It was Thomas Aquinas who argued that "self preservation is natural, and a private individual may not intend to kill an attacker even though the death of the assailant may result."

For about 800 years of Christian tradition, killing someone in self defense was considered excessive self love.  

If this was the case, why then do we see non-violence (and to a greater extent pacifism) as not real answers to the complex situations we are in?  

Have we fallen into excessive self love?