It is an idealistic ethos. In my mind it's as naive as centrally planned socialism, but just at the other end of the spectrum.

I fail to find ethics in libertarianism. Unless you're talking randian ethics, which are a far cry from ethics themselves.

Far from it. Libertarianism is the most realistic and non-naive system around, exactly because it is the one system that does not pretend that we can fix all the flaws in human nature and socially-engineer a perfect society by just passing enough laws and creating enough rules and regulations and bureaucracies.

At it's core, libertarianism makes no statement about outcomes, but simply demands that people be free to make their own choices without being subject to force or fraud, and are then responsible for the outcome of their actions. Nobody is making any Pollyanna'ish guarantee that such a system will result in the most possible desirable outcome for everybody involved. The claim is that it's just the right thing to do, that most people will be better off (economically) than under other systems, and that you accept that every system - this one included - has its pathologies. You can't get much less naive than that.

"The claim is that it's just the right thing to do, that most people will be better off (economically) than under other systems"

There it is, that is the idealistic part.

Not really. I mean, economics is mostly voodoo science anyway, so it's hard to make a lot of objective statements about any of this, but it's hardly a stretch to suggest that laissez-faire free-market policies are generally better for economic growth.

But, again, none of this is really the point. Every system is flawed in its own ways, and the libertarian approach simply acknowledges that, rather than trying to distort reality and pretend that a "perfect" system is even theoretically possible.