All the changes come with a price. U.S had its own civil war. Compare South Korea with North Korea.
I believe the Iraq story went so bad because the invasion was based on a lie so once Saddam was killed there was nothing left to do(based on the initial plan). Even so in the long run it might prove to be a good thing for Iraq.
As far as I'm concerned all dictators must die. People have the right to be free. We should just make sure the price is not too high and take more responsability to handle things once the top dog is put down.
Iraq and most of the middle east was already is a big mess. Look at the rate of illiteracy in Afganistan. These people live in tribes. They execut/ed people in public markets. You can't expect them to organize themselves as soon as the ruler is out. They need leadership and infrastructure(i.e education, jobs) that the U.S never planned to provide.