Karl Barth's most important contribution to the church is not this or that doctrine, but a way of doing theology. This way begins with the being and action of God as revealed by the person of Christ. This being and action of God is what is really real. Human being and action is only real to the extent that it corresponds to the divine. So, for example, we do not know what a father is, and then understand God in the light of our experience or practice of fatherhood. Rather, we know God as Father, and human fatherhood or lack thereof can only be seen in this light. Human fatherhood is first of all judged and then redeemed by the Fatherhood of God. Or better, first of all redeemed, and then judged.
One of Remembrance Day's effects on the church is the undoing of Karl Barth's contribution. On Remembrance Day we begin with a human understanding of sacrifice, and in the light of this we understand "the greatest sacrifice" offered by Christ. In churches up and down the UK, the relationship between Christ as Lord and the church as servant is reversed. We remember our deeds and judge Him on their terms, when we should be remembering His deeds and opening ourselves up to His gracious judgement. On this day of reversal we forget that Christ was the collateral damage of a foreign occupation conducted in the name of peace, and that he suffered at the hands of those who sacrificed their lives (and the lives of their enemies) for the empire.
One does not need to be a pacifist, then, to oppose the "celebration" of Remembrance Day within the church. One only needs to pay attention to the proper logic of Christian talk about God: a logic based on the truth that when we talk about God we are not talking about a greater version of ourselves.