Let me ask you: If wars could be prevented - I'm all for it, but would you just let an enemy come into your land and kill your loved ones? You just roll over and let someone rape and plunder your household? If the Jehovah's Witnesses had their own country - I guess they would only pray that noone invades them, right? Otherwise, they would just do nothing? It's so easy to say "war is bad" when you don't lift a hand to protect the fight for the freedoms you are obviously take advantage of. Maybe one day we won't have war ... that would be nice, but until that day comes ... you should be thankful for those who protect your freedom.
I can understand the point you make about someone coming into my house to kill, rape, and plunder. I would need to protect my family as much as I could. My goal would not be to kill, unless that is the only option. However, this is different when it comes to the country in which I live because of the following reasons:
1) The country is not my family. While I respect the government, I choose to not be involved in it's affairs.
2) There are people that will fight. They do not need me. Consider also, if everyone was one of JWs then there would be no war, and thus no need to fight.
3) Most wars involve killing innocent people. How could I have that bloodguilt on my hands? What would happen if I killed a fellow believer? I could not put myself in that positon.
3) There are some situations when yes, one needs to do nothing, just as Jesus did not fight and instructed Peter not to.