Alan Greenspan might have been one of the big reasons America did so well throughout the 80's and 90's. He lectured congress constantly on the evils of government spending and economic intervention, and probably helped chart a wiser course for our monetary policy through his position at the FR than we would have otherwise had.
I believe he felt it was his moral imperative to undertake the responsibility he did, because if it wasn't him, it would have been some other idiot.
His virtues don't immunize him from philosophic hypocrisy though, and he was ostracized by the objectivist crowd he once associated with for his professional decisions.
I don't think Friedman was as "pure" a libertarian as we all wish he was. I've heard him say some stuff that I definitely disagreed with. I still like the guy though, and so did Ron Paul if C-SPAN is any indication.