While I can see what the question’s supposed to get at, I don’t think it’s a very interesting one to ask. None of us ever has all the information we need before making an important decision, and none of us ever knows all the future consequences it’ll bring.
The crucial question isn’t what would one do if one had all the information we have today — the crucial point is that the Iraq War demonstrated how wrong things can go when governments implement dramatic policies based on incorrect information. Indeed, the government never has all the right information, and politicians ought to know this.
The gap between what was projected to happen in Iraq and what actually happened — including the shift in public opinion about the war — occurred in part because President Bush didn’t weigh heavily enough the possibility that his information was incorrect; that things on the ground wouldn’t go as well as planned; that nation-building would fail as it almost always does; and that the American people wouldn’t be supportive of an effort that drags on way longer than expected. Of course, members of Congress did the same thing. And this isn’t unique to President Bush and the war in Iraq.