In his book, “The Counter-Revolution of Science”, Hayek argued against scientism – attempts by the social sciences to ape the methods of the natural sciences by ignoring the subjectivity of economic value. I will apply these ideas to criticise of some current ideas that the government should use force to make people happier. So what was Hayek’s argument against scientism? Economics explains how a person acts by looking at his actions as being aimed at some end. For example, if you look at all of the objects that people call hammers they don’t have much in common. The reason why a blocky object made out of wood and another made out of titanium are both called hammers is that they are both used to hit things. So if we try to solve economic problems concerning hammers by looking for some physical feature that all hammers have in common to explain their value we will fail. In other words the value a person places on something is due to his subjective estimate of how well it fits his ends and not due to some fixed standard that can be objectively measured.
Now let’s suppose I offer Jack a choice between a carrot and a chocolate brownie and that Jack chooses the carrot. Then Jack prefers carrots to brownies, right? Not necessarily. If Jack thinks carrots are less healthy then brownies then he might eat carrots instead of brownies because he wants to live longer. If I offered Jack a brownie and a pill that eliminates all of the adverse health effects of eating brownies then Jack might choose the brownie. So Jack doesn’t just choose between the carrot and the brownie, he chooses between the problem-situation he ends up in after eating the carrot and the problem-situation he ends up in after eating the brownie.
Now let’s suppose that I’m really fanatical about health and to keep Jack healthy I threaten to brutally torture him to death if he chooses the brownie over the carrot. I might claim that I am just making a choice that will get Jack to take an action that he would take if he were better informed. However, I am preventing Jack from eating the brownie and so preventing him from refuting my ideas about how he would act if he knew what I know about the horrible health problems caused by brownies.
Another thought experiment: Jack decides that he doesn’t care about the health effects of brownies and eats lots of them. Toward the end of his life, lamenting his poor choices with respect to brownies, Jack might say that he wishes that he hadn’t eaten the brownies. He might even say that he wishes somebody had forced him to eat carrots instead. However, this is pure speculation. Jack had a lot of fun eating brownies and was happy and productive as a result of that. Maybe if I forced Jack to eat carrots he would be miserable and unproductive. Maybe eating brownies was the best he could do given the knowledge available not just to him but to anyone who might force him not to eat brownies.
Many anti-liberty people like to say we can measure happiness with surveys and then force people to adopt policies that will lead to more happiness . For example, we should have high taxes so people can’t choose to make a lot more money because more money doesn’t make people happier until you get some ridiculously large amount that most people will never get, so without the tax people will just work harder without getting happier. What does this policy do? People are not allowed to decide they don’t want to pay taxation to their government and would prefer to buy a different bundle of services from different people. This is policy idea is scientistic tosh.
By following such policies the government would prevent people who disagree with the government’s evaluation of what their priorities ought to be from acting on that disagreement. So this theory is not testable because it prevents the only means of testing a person’s preferences: allowing him to choose a different option.
The notion that charging people more tax will make them happier in the long run in some vague sense is pure speculation, just like the carrot/brownie speculation. Perhaps people in the happy tax society would be happier if they lived in a society in which ambitions are not squashed by the government. Or perhaps some people are lying when they say on their deathbed that they wish they had spent more time with their family because they think it will make their family happier or more kindly disposed toward them. Perhaps the government doesn’t know how to make people happy.
 I could just stop at this point and say that I don’t see why maximising a particular psychological state is such a big deal. I could also say that even if maximising happiness is the most important thing in the whole universe I don’t see why the government should get to dictate what counts as happiness and how people should pursue it. But let’s just take for granted that these problems have been solved for the sake of argument. It’s a ridiculous assumption, but granting it and then demolishing the anti-liberal argument just makes anti-liberal policies is a more effective criticism.