If someone says they're "against war", then just ask if they thought WWII should have been fought, or the Civil War. The Civil War actually killed the highest percentage of Americans of any war, and created huge civilian suffering in the South. If they are for either of these wars, then they're not "against war". Period.
When you point this out, they'll say "We had to oppose Hitler". Just reply that the particular reason they are for having fought the war is irrelevant. If they are for any war that's been fought, they're not against war. They're just against this particular war. Everyone can claim to be against war if you limit it to wars they disagree with. I was against our war in Kosovo and I supported the Gulf War, so I guess I can claim to be "against war". Don't let them get away with this "I'm against war" BS.
This is similar to Orwell's position: You cannot be a pacifist when your country is attacked. It is very shallow to think that one is morally superior in taking a non-retaliatory posture. And, moreover, pacificism under circumstances such as these is very dangerous -- and immoral. Would these same people be pacifists if the threat were from Hitler? Or would they contrive some criticism of their own country to justify Hitler's actions? These people need to think...
The end result of pacifism under these circumstances is to support Bin Laden or some other monster who will continue to attack and eventually destroy us in the name of tyrrany.