One of the things I am convinced of should be a hermeneutical principle is refusing to flatten the scriptural witness on an issue. This is why I'm convinced a biblical argument for pacificism needs to be carefully nuanced, and take full account of the flow of the redemptive meta-narrative that stretched from Genesis to Revelation.
It's also why I'm fully willing to concede that the Old Testament condones, and in some instances depicts Divinely mandated, war. That is then why I'll only make an argument for pacificism ultimately from the New Testament, because I believe the New Covenant and the Incarnation, and more significantly, the pattern of the Crucifixion and Resurrection, is decisive and transformative on the issue of violence and war.
Then, one must come to terms with the military language and martial metaphors resident in the New Testament. How does one do that? I think it is far from satisfactory to cite the presence of militant language as a case for militancy from the New Testament. To do so is to miss the significance of metaphorical language.
I would suggest, that a careful reading of metaphorical violent language in the New Testament corpus routinely subverts physical violence and transfers the referents of conflict to 'spiritual' matters. That, in effect, is what metaphors deal in: semantic transference. Ephesians 6 is the classic example of this, and Eph 6:12 is the verse that keys you in, not "against flesh and blood".
It is, indeed, not conflict that the New Testament rules out, but violence in particular. In doing so, in a Christocentric fashion, there is no room for martial metaphors to reverse that ethical innovation. One can't argue back from metaphors to the normativity of violence, if the non-metaphorical has already ruled it out.
The Revelation to John is the book that contains probably the most significant, forceful, and ambiguous metaphorical language about violence (if metaphor is even the proper catch-all). Yet, there more than anywhere, I'd argue that the whole book systematically undermines and subverts the paradigm of a conquering military messiah. The contrast of the Lion of Rev 5:5 with the slaughtered Lamb of Rev 5:6 is the most succinct summary of a pattern that the book repeats throughout.
A secondary implication though, is to note that the NT doesn't do away with militant metaphors. Unless one has embraced a position that is radically against the arts on other grounds, it is not the presence of violence in film, literature, even video-games that is the sticking-point, but where that violence points to. To take a non-allegorical text, the Lord of the Rings is interwoven with Christian themes, but is not an explicitly Christian text, and manages to portray a world of violence without glorifying violence or providing violence as the ultimate solution. As Christians wrestling with the issue of metaphor and violence, or more deeply with the Cruciform pacificism of Jesus, we would do well to reflect more deeply on these matters.