Unfortunately I think the answer is yes; but why?! I hear you cry. Surely Stuart can't hold this alarmist (lefty?) position!
Well, we've already invented some pretty cool weapons that can kill millions of people in a few minutes. This is scary and no matter how wrong the war enthusiasts were about Iraq it is still very undesirable that bad countries have them. Especially countries with insane/evil leaders. For the moment WMD are both difficult to make and very expensive, but the way things have been going is that people get richer and technology gets cheaper. As long as this is happening it's more likely that some deranged lunatic will get his hands on a bomb and blow up lots of people.
Not too far in the future it's likely that new weapons will be made that are much more destructive than the weapons we have now. Weapons that could wipe out all life (including cockroaches). If countries like North Korea get these weapons or even fail to regulate their own population properly we'd all be in great danger and preemptive war could be the only way to deal with it.
If the Iraq war had been a success it would have acted as a powerful deterrent to other governments messing around and public opinion would be less hostile to the concept. It's now a much tougher sell and that's dangerous.