Utilitarianism is concerned with consequences and thus properly applied doesn't violate freedom.
The problem with collectivist utilitarian justifications is they do not include in the calculus the consequences of their own interventions in the name of changing consequences.
If the analytical and empirical understandings are valid they must converge if they result from reality.
I can either understand the law of gravity, or I can watch a rock fall. If my observations are not clouded or if my understanding of physics is not flawed I will conclude the same thing.
Keynesianism and collectivism have in common that they ignore the consequences of their own activities. When you impose an immoral order in the pursuance of what you consider to be a moral goal, you may achieve the immediate end, but you have imposed immorality on the system as well. The genuine consequentialist is not surprised by this.
The faux utilitarian actually rejects utility when it contradicts his religious belief in the state as creator of order. It is in fact a belief that entropy can be conquered. It cannot. Social order can only be imposed in spatial and temporal vicinities at the expense of greater disorder in others and in the overall net increase in disorder.
The suspicion of the ancap is that only in the absence of attempts to impose order, will order will be optimized. And this is not to say there would be no disorder, just that only in this environment can the most order possible be achieved.
The reason that more free societies prosper and have less disorder than less free societies is because they attempt to impose less order and thus profit from more order.
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