If the people of Iraq really want Saddam out of office, they will do it.
See what happened in 1989 with the Iron Curtain, see what happened in Greece, Spain, Portugal. When the people are really fed up with a leader they get rid of him.
That sounds more than a bit optimistic to me. Some dictatorships are so brutal they are practically impossible to overthrow from within. Uprisings will occur - and be suppressed in bloodshed. If they exist long enough and that happens often enough, entire generations will give up even trying, and accomodate as well as they can instead. I don't think the North Koreans, for example, have any chance. In Iraq, uprisings did occur, like that of the above-mentioned Shi'ites, but were bombed down, end of story.
The powerlessness can be especially great if it's a territory or country that's occupied by another. For certain only a tiny minority of Lithuanians, Estonians and Latvians was ever sincerely loyal to the Soviet Union, but what were they to do? Their guerrilla fighters as well as 10% of the rest of the population had been deported to the camps. Should they rebel, only to be faced with a new period of state terror, like the Hungarians were after '56?
I wouldn't think Saddam is supported by a lot of Iraqi's. If outside of the clique deriving wealth or power from the current regime anyone will do anything to stop the US troops, it will be out of fear of the 'unknown danger', as you say.
The countries you mention threw off dictatorship as soon as there was a reasonable chance
. I think it should always be our repsonsibility to create as many of such chances as possible - in so far as doing so is reasonably responsible, in that it does not incur dangers or suffering greater than the dictatorships in question pose.