(Following up on a previous post about worst case scenarios...)
The people who find the worst case scenarios to be persuasive reasons for action on climate change are likely the opposite ones who would use the same reasoning to argue for a continued military presence in Iraq.
Despite thinking we should get out of Iraq, I also agree that potentially, things could get much worse there after we leave. So why leave?
One argument would be that we're just putting off the inevitable - we're going to leave sooner or later, and even if the worst case scenario occurs, all we do by staying is add a lot of death and destruction in the meantime. Not a bad argument, but the counter is that staying can buy time to find a solution.
Another argument is that things can get worse with our troops there. I wouldn't disagree, but I don't expect it would get as bad as in some full-out genocide/civil war.
A better argument to me is that for the US and the rest of the world - basically for everyone except the Iraqis - right now is the worst case scenario. I don't think an Al Qaeda takeover of Iraq is a credible scenario, and even if it was, the current cost of 1,000 dead Americans and $120 billion annually exceeds the damage rate that Al Qaeda could do to us. As for the rest of the world, having the US in Iraq only creates problem. Only for the Iraqis could the situation get much worse.
The best argument though is that you shouldn't just look at the worst case scenario. I think Iraqis have a shot at things not getting worse but rather staying at the same awful level they're at right now, and after a decade or so, slowly improve and follow Lebanon's trajectory. I don't see any other path for improvement. For the rest of us, we're clearly better off if the US gets out. And the Iraqis want us out. It's time to leave.
I lost the climate change thread here, but I think a similar reasoning applies - making a decision solely based on worst case scenarios is a bad idea. The medium case scenario for climate change still describes a crisis, though, providing plenty of reasons to take action.