The problem with many attempts to maintain a stance of just way is that the follow a pattern of OT ethics that is radicalised in the NT. In the OT ethical concerns are largely confined to the covenant community, and while some of those concerns are extended to the "alien in your midst", generally non-Israelites are treated as "other". One temptation of those defending Just War is to read a similar pattern into the NT - that christian love and non-resistance is practiced primarily within the covenant community, and only be extension to outsiders. There are two great flaws with this thinking. The first is that very few Just War thinkers are prepared to constitute the Church as a political entity like Israel was, and to follow through their logic. If they did, they would be forced to leave their homes and take up arms for their persecuted brothers in Africa, the Middle East, and parts of Asia. One cannot take up arms to defend one's nation if one isn't prepared to take up arms to defend the church.
The second, and greater flaw, is that Jesus radicalises the concept of 'neighbour', and while the NT maintains boundaries of inside/outside the covenant community, more and more the distinction is one of discipline and primary care, not a duality of ethical stance, so that the bombshell of the Good Samaritan parable is predicated on the idea that the love of neighbour excludes the outsider, and Jesus' radical idea is that not only is the same ethical stance to be taken towards the outsider, but in his story it is the outsider who takes the right ethical stance at all. For Jesus, love of neighbour is no longer an idea that reaches a limit within the community, but is a love that extends as far as it is able.