I agree that calling it fiat is not arguing against it, but it's important because there are a large number of people who are deep in the bitcoin world, and get infected with a little bit of the Libertarian/gold-standard mentality that thinks fiat is a bad word. In the end, everything that isn't a direct barter exchange of usable goods is a fiat currency, because that's the POINT of an exchange medium; something that everyone agrees is worth something in order to facilitate trade, it makes life easier. Pointing out that bitcoin is just as much a fiat currency as the dollar or the euro or gold helps dispel the misconceptions about currency and helps people learn more about bitcoin and currency as a whole.