It's not that I think a world without war would be a bad thing, it's just that I think the notion of humanity living in peace on this planet is pretty damn far fetched.
Generally, the reasons that man has gone to war over are pretty stupid when you think about it. We kill each other over interpretations of and idea that is imperceivable to man (God). We've slaughtered each other over the right to own slaves. We've even gone to war to stop a country from choosing its own form of government, just to satisfy some antiquated policy notion of "containment (Vietnam).
Don't get me wrong, though: every person has a right to defend themselves and what belongs to them. So it's not as if all wars have been completely unjustified. Unfortunately, the whole question of "what belongs to whom," is where matters start to get out of hand. If some clown thinks he can stroll in to my home and just help himself to whatever he wants because he's more racially pure, or because God told him he could, or because it's just natural that he get my stuff, then that fool is going to have a fight on his hands.
When you understand war in its historical context, the whole idea seems absolutely insane. I guess it's less ridiculous prior to, say the 14th Century, but when you think about war in the modern era it just boggles the mind. For about 500 years now, humans have largely considered war to be just another step in the international political process.
You go to the negotiating table, make your demands, try to bob and weave without looking like too much of a jackass. When talking doesn't work? Well, you resort to sending wave after wave of your people at each other as little more than meat shields until one side can't take the horror anymore.
In normal one-on-one human interaction, a situation that breaks out into a fist fight is generally considered to be faux pas by today's standards. When a brawl goes down, everyone has the mind set that one or both of the parties became unreasonable at some point and just couldn't resolve things like a rational person. For so long, this was considered an acceptable outcome for international disputes.
Knowing just how irrational human beings can be, seeing that we can bring unbridled death and destruction upon our own race, it's fairly pie-in-the-sky to think that there will ever be any sort of real peace. We'd have to be a society akin to Brave New World in order for the violence to stop, and I don't think that's an existence anyone in their right mind would want.