I do have to refute that idea. I'm not sure how much their opinions matter and if my time is well spent trying to change them, but they're in my life so I collect the evidence.
And, of course, some Libertarians hold both beliefs - that free markets are the moral approach AND that the create better outcomes more often than not. But other than maybe a few n00bs who just discovered Libertarianism from a pamphlet or something, almost nobody is going around claiming that free markets fix everything.
If you construe some tipping point like for example chance of existential or utilitarian failure that does justify coercion how do you differentiate between a society in which minimizing coercion is the goal and one in which whatever you construe as justifying coercion is actually the guiding principal.