Americans get into wars when it suits their needs and interests. There are lots of countries around the world that have dictatorships and that violate human rights. America chose to invade Iraq because Iraq's got oil. If you stabilize Iraq, you stabilize an oil source that fuels the growth of the American economy. Let's not forget 9/11, either - some Americans were in favour of the war in Iraq because they believed that the Iraqi government was somehow involved in 9/11, although there's no concrete proof of this theory. In other words, the war in Iraq made it look like the American government was doing something to retaliate against the the attack on the United States, although it was never officially fought for that reason. Strangely enough, though, the government never corrected people who thought otherwise. I don't agree with the Iraq war and I never have, but it does make sense in a way. Every country wants to secure its economic interests.
Iraq is like Vietnam in that Iraq's culture is very different from that of the United States, and the Americans rushed into fighting without a good idea of just what they were getting into. People in Iraq fight differently from people in the United States. They also think differently. The Americans thought that they could fix Iraq using pure military force, and this was a big mistake on their part.
Although the American operation in Iraq is certainly failing, you also need to consider the successes of the operation. They did manage to overthrow the dictator - at least give them that. Now they're left in a country with little infrastructure and complex social problems that they can't profess to understand completely. Of course they're having trouble! Most Americans I know now realize the shortcomings of their foreign policy.
With all that being said, I don't think that you should be hating so much on the United States. Lots of Americans don't agree with their government's spending policies. They wish that they could have better funded social programs. The problem is that the United States has gotten itself into a tight spot and has lots of enemies. They can't just scrap their military. Even if the U.S. isn't the best at everything they do, lots of people still want to live there. All countries have their problems.