I hardly know where to begin with the "Bush Doctrine." It should be obvious that you can't just decide to invade and attack any country that you (unilaterally) decide is a threat to you. At least not if you want to be seen as a peaceful, friendly nation as opposed to being a dangerous rogue state.
I think the obstacle for Americans in understanding this is a failure to see what it looks like from an outside perspective. "America is the good guys; America is a democracy whose actions I can vote for; America will ultimately be acting in my interests as an American; therefore America can be trusted to use this power wisely." I think that about sums up the reasoning for why it's okay. Now (if you're an American), I'd like you to try a little thought experiment of imagining that you're not an American, you can't vote in the U.S. election, and you have no reason to believe that your interests or perspective will be taken into account the next time the "America First" party decides who to bomb.
Obviously the Bush Doctrine relies on having one set of rules for the U.S. and a completely different set of rules for every other country. If every country were allowed to attack any other country that threatens their security, then Iran would be justified in attacking the U.S. already, and that would be just the beginning of the free-for-all of international destruction.
Now I know that some people will immediately dismiss me as a cowardly European, relying on the safety provided by the U.S. military without showing any gratitude and yadda yadda yadda. So let me explain myself a bit:
I'm an American, born and bred. I'm not motivated by hatred for America. I want to be proud of my homeland. I want my homeland to be the good guys. If America has chosen to be "the world's policeman" so be it, but launching unprovoked attacks on other nations, capturing foreign nationals and holding them without trial and torturing them -- these are not the actions of "the friendly cop on the beat." In order to find terrorists worldwide, in order to find and neutralize dangerous weapons that are floating around the world black market, in short to "win the war on terror" it is critical to have the trust and cooperation of lawful people worldwide. Thanks to the Bush Doctrine, lawful people worldwide are terrified of the U.S., and with good reason.
It's hard to exaggerate how sudden and dramatic the shift in world opinion has been. In talking with colleagues from all over Europe, those who have visited the U.S. universally speak of their experiences fondly, and they express surprise that I would choose to live in Europe instead. They also express shock and bewilderment at the current American foreign policy. These are people who would like nothing more than to view the current dismal failure as a fluke. It wouldn't be too difficult to regain their trust and affection if the American people were to stand up and demand a foreign policy that is more constructive, cooperative, and fair.
It's time to stop imagining that "American interests" is just another way of saying "goodness and virtue" and to stop assuming that foreigners don't deserve the same standards of fairness and justice. Remember that to people in other countries you are a foreigner. Trust and esteem aren't earned merely by having the name "America," they come from being fair and trustworthy. These things are earned, with effort. Let's make that effort.
Let's be the good guys.