Libertarians are quick to argue that socialism leads to fascism.
However, it is actually the opposite, Libertarianism leads to fascism.
Why is this? Politically, liberals are for regulating business and giving more benefits to the middle class and poor. For example, the government spends the bulk of it's money on transfer payments to the poor and elderly (most developed nations spend even most on these things). And the bulk of it's regulations are on consumer, worker and environmental safety.
If these things are removed, then there is nothing in the way to stop corporate fascism. This is not a hypothesis, it actually (almost) happened, as Thom and others reminded us in the failed 1934 coup attempt.