> I've always thought that libertarians and free-market extremists are some sort of outliers on the morality spectrum - probably sitting near the extreme low end of the axis

That's funny, because I'd think it the exact opposite. The linchpin of most libertarians, the non-aggression principle (NAP), is pretty much all about morality. It might not be correct, especially with the sticky issue of defining property rights and whatnot, but it certainly aspires to be a moral framework.

A libertarian would say it's not moral for you to take resources from the "haves" by force and redistribute it to the "have-nots" just because you think it's for the greater good; morality is achieved by voluntary cooperation. Basically this: http://i.imgur.com/vmMrN6O.png

The people I know who donate significant sums lean libertarian.

As true as that may be, it's anecdata, and not necessarily representative.