When left with a minimum level of governmental interference, individuals pursue what they believe is in their own rational self-interest. That's not libertarian BS. Moreover, it's the statists who think that government's role be expanded and individual liberty curtailed in the name of some amorphous good. In other words, one's rational self-interest should be determined by someone else. That's BS.
Regurgitated libertarianism. We have a bloated Federal government and it should pursue policies abroad that are in our self interest. Such as lowering our trade deficit to avoid a dollar crash. But instead the Feds are doing all kinds of other things they shouldn't. They won't even defend our Mexico borderer
But the modern economy is—unfortunately— too large and what it produces too complex, to leave all decisions to the marketplace.
That would be true except for two things.
1) People often pursue irrational self-interest such as smoking, not wearing seatbelts, going through life 40 pounds or more overweight, etc. (I choose these examples because they are not controversial in the context of this thread.)
2) The societal costs of irrational self interest does affect other people considerable, giving them incentive and in some cases the duty to react.
Libertarianism is based on an idealized version of human interactions.
Cheers!