What to do if you fall into a conversation with someone about the terrorist attacks who doesn't believe in retaliation:
1. Engage in conversation, and ask if military force is appropriate.
2. When he says "No," ask, "Why not?"
3. Wait until he says something to the effect of "Because that would just cause more innocent deaths, which would be awful and we should not cause more violence."
4. When he's in mid sentence, punch him in the face as hard as you can.
5. When he gets back up to punch you, point out that it would be a mistake and contrary to his values to strike you, because that would be awful and he should not cause more violence.
6. Wait until he agrees, and has pledged not to commit additional violence.
7. Punch him in the face again, harder this time.
8. Repeat steps 5 through 8 until he understands that sometimes it is necessary to punch back.