it is not "introducing" democracy. It is "forcing" democracy. Furthermore, there is no precedent that forcing a nation to adopt democracy has ever worked, no matter how hard the British (to name one example) tried. In fact, no forcing of any culture on a nation has ever worked.
Much of the intellectual justification for the war has come from the writings of Bernard Lewis, a professor at Princeton. His writings on the Middle East and Muslim culture have inspired neoconservative firebrands like Richard Perle, Paul Wolfowitz and Dick Cheney. However, these guys seem to have have skipped over Lewis' early writings, which were much more cautious.
In the 1950's, Lewis wrote about the long-standing resentment at being overtaken by the West which fuels the Middle East's "Muslim rage." He argued that the West "should take as little action as possible in the Middle East, since we of the West should beware of porposing solutions that, however good, are discredited by the very fact of our having suggested them."
In 1991, he wrote about the "age-old autocratic traditions" in the Arab world, and warned that there is "no guarantee that efforts to democratize will succeed, and even if they do, after how long and at what price."
He also wrote: "Democracy is dangerous anywhere. We talk sometimes as if democracy were the natural human condition, as if any deviation from it is a crime to be punished or a disease to be cured. This is not true."