In other words, he (John the Baptist) says, "Being a soldier gives you extraordinary power. Don't abuse that power by extorting money or falsely accusing people." Through Christian history, most Christians have chosen to take a similar approach regarding war. It's not that Christians should be pacifists, they say, but we shouldn't abuse power--including the power of weaponry. We may still have to go to war, but we should be just and restrained in the way we conduct ourselves.
Others, though, have not been satisfied with this approach. they have looked at Jesus' kingdom manifesto, and they have felt it is impossible for a person to simultaneously put Jesus' teachings into action and participate in war.
McLaren, 'The Secret Message of Jesus', pp. 150-151
That, in a nutshell, summarizes the whole problem with emergents (though to be fair, they are not the only ones who are not 'satisfied' with the Bible's words and try to add to them).
You will not find any place in the New Testament were a radical (I hate that word) pacifism is either commanded or encouraged; in fact, in the three instances where John the Baptist, Jesus, and Peter had dealings with military personnel (John giving advice to soldiers, Jesus healing the centurion's servant, and Peter at Cornelius' house to open the door to the Gentiles for the Gospel), we see no condemnation at all of the military. John does not call them 'brood of vipers', Jesus commends the centurion as having more faith then any He had seen in Israel, and Peter is send by God to Cornelius.
Factor in, then, the Old Testament, and we can say that the pacifists must add to what the Bible says in order to support their position.