I think the point of the article and the research that it cites is that most people, even if they don't carry a balance, qualify (in your terms) as "dumb" since they spend more when they use a credit card than they would have had they used cash. A subtle and subconscious effect, yes, but one that has been measured in some decent experiments.

Anyone can see that carrying a balance at 18% interest or whatever isn't a good idea. But what's harder to discern is just how much more you are spending with a credit card since it removes, temporally, the pain of paying from the delight of receiving some good or service. I'd be the first to admit that I likely overspend using a CC versus using cash. Hard to resist.