I see all these people calling themselves libertarians arguing against BTC but I have yet to see why BTC would fail.

I hate this "BTC is not money" argument because the core foundation of liberalism states basically "money is what people voluntarily choose to use as money". So if they are convinced that BTC works (works at least better than some alternative) , why shouldn't they use it as money?

Volatility is not an argument. Before "adoption" of USD and gold as money, they most probably were volatile as well...