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I think you're applying a very single minded and obtuse approach to military action and the reasons for going to war.
The reasons to not apply the same logic for one country as opposed to another are many and have more to do with logistics, troop safety, estimates for success, etc than the simple moral decision to act. Imagine your reaction when 50,000 troops laid dead in NK "well, at least we applied our morals evenly!". You should look at each situation as just that - a single situation that needs to be dealt with on it's own merits and circumstances.
Bush is no hero but he was President during the single worst invasion and tragedy our country has faced. To say "well, he said he was against nation building when he ran for office!" is anemic and ignores any person's ability to change their decision making process based on current events.
I am no fan of Bush. I think he did many if not most things wrong or against my own views. I don't come to my current views on the war without first feeling it was wrong top to bottom. But, I had to ask myself if I thought us NOT intervening in Rawanda was wrong. I think it was. I also think we did the right thing by acting to stop the Bosnian conflict.
Given those two items, I have to ask myself - should we have acted in Iraq - I think yes. Should we have acted in NK, I think yes but, not the same way we did in Iraq. I think our actions so far in NK have (now, thankfully) resulted in progress. Different situations, different actions but, to me, both right.