One of the many paradoxes of behaviorism is that the only way you can tell that Arnold Kling and I disagree about it is from our words. Observe our behavior for a hundred years; you'll never figure out where we stand without listening to us or reading us (or at least reading our "body language"). Lots of positions in philosophy have been called "self-refuting," but behaviorism is near the top of the list.
However, after carefully reading Arnold's words, I disagree with less than one might expect.
Seriously, I think that behaviorism is a reaction against two propositions. One is that we need to examine whether people really optimize.
I agree that we do not "need to examine" whether people optimize. Treat it as a tautology, I won't demur. But we DO need to examine what they optimize. Do they maximize what really is in their narrow self-interest? Do they maximize what they falsely believe is in their narrow self-interest? Or are they not even trying to maximize their narrow self-interest? These are interesting questions, and unless you listen to people, observing their behavior probably won't answer them.
The other is that we need to observe people's utility functions.
I agree that we do not "need to observe" people's utility functions. Good thing too, because with the exception of one's self, that would require telepathy. But is listening to other people a helpful way to learn more about their utility functions? I say it is.
The doctrine of revealed preference, which I associate with Samuelson, says that we do not need to observe utility functions. Instead, we can infer relative marginal utility indirectly by observing choices.
Yes, we can infer relative marginal utility (in a textbook ordinal sense) by observing choices. But what opponent of behaviorism ever denied that? The real behaviorist position, though, is that observing choices is the ONLY way to gain information about utility functions. Otherwise, they would not object when other economists conduct surveys.
A short way of putting this form of behaviorism is "watch what people do, not what they say." For example, so-called "happiness research" will come up with results that say that people get little or no incremental happiness beyond $20,000 of income. Yet their behavior contradicts that, since many people could easily cut back on work and still have $20,000 a year. I believe the behavior, not the surveys.
Does their behavior really contradict their answers? Only if people maximize their own happiness - as philosophers would say, if psychological hedonism is true. Common sense and my introspection say it's not true. People opt for less personal happiness all the time. Sometimes, of course, they are trading off happiness now for happiness later. But other times, they are trading off their own happiness for the happiness of others. Or they might give up some happiness to have more kids, more success, or more neuroses.
Personally, if happiness research didn't find a small effect of money on happiness (for people who are already middle class or richer), I wouldn't trust it. A vast increase in income hasn't made me much happier than I was in grad school. And I see lots of rich workaholics who never crack a smile. Their money brings them lots of happiness? Gee, I'd hate to have known them when they were starving students. They must have been suicidal!
Incidentally, if humans really maximized their own happiness, there would be a big evolutionary puzzle: How come with have so many emotions when we only obey one? Why do we feel curiosity, for example? You could try to reduce curiosity to happiness, but that's implausible. I've felt curious and sad at the same time. Haven't you?