[mikeash]

You're right that smart people can sometimes act stupid, but there are so many situation where we blame people for their inherent intellectual failings.

For example, smart people frequently describe the lottery as "a tax on stupid people" in a sneering way. When people get taken by an obvious scam, we often place as much if not more blame on the victim as we do on the scammer. Or look at the Darwin Awards for numerous examples of people basically saying that others deserve death for being dumb.

Sure, there are examples where a smart person is negligent, we describe that as "stupid," and we rightfully blame them for the consequences. But there are many more examples where a dumb person doesn't understand that what they're doing won't work, it fails predictably, and we say they deserve it. Lotteries, scams (but I repeat myself), avoiding insurance or banks, and much more tend to fall into this category.

If someone got robbed because they had a bad leg and couldn't run away, we'd sympathize. If they got robbed because they had a bad brain and couldn't detect that this smooth-talking stranger was scamming them, we'd tell them they should stop being so stupid.