How do you interpret the Luke passage?
It can't eradicate the Sermon on the Mount if we're to take seriously the notion of Scripture being God's word.
Another time Jesus mentions swords is when he said he came not to bring peace, but a sword. Yet we must somehow interpret that in a way that's consistent with his saying "blessed are the peacemakers."
To Jesus, the sword represents the tool of spiritual warfare, of God bringing people from darkness into light and leaving their old ways behind -- not adapting their faith to the world, but adapting themselves to the faith.
If you have another way he means "sword" that's consistent with the SotM I'm all ears.
My basic point in all this is not that we should simply turn the other cheek to the Islamofascists. Jesus is setting out ideals, not things that we can achieve right now. The trouble lies when we forget what the goals are and revel in our earthliness and fleshiness.