It might be a superior means to store value. The theory is that is as the amount of dollars (or any fiat currency) constantly increases, anyone holding large quantities of dollars will want to exchange them for something with a more fixed supply. Usually this is stocks. Oil futures, property, and gold are also used as stores of value. (In countries with weak currencies, people also hoard dollars as a comparatively stronger source of value).
So the purely monetarist argument says if there are only 21m bitcoins, and an ever-growing amount of dollars, one would expect that the dollar price of bitcoin will only be stable at 0 or infinity. E.g., either the network crashes and bitcoin becomes worthless, or the dollar collapses and bitcoin reigns supreme.
http://nakamotoinstitute.org/mempool/im-hoarding-bitcoins-an... - see here for more on this theory as regards bitcoin.
The counter to this argument is that a. despite seeming logical, money supply inflation doesn't always seem to occur in reality. E.g., quantitive easing hasn't noticeably increased consumer prices.
b. Bitcoin is volatile, which means it isn't actually a safe store of value. One persuasive argument I heard (from goldbugs) is that bitcoin, having a fixed supply, has no mechanism to stabilise the price, and so booms and busts become self-reinforcing. With gold, on the other hand, the amount mined varies depending on the market price, which smoothes out booms and busts.
I'm expecting both gold and bitcoin to increase in value over the next ten years as the EU and US both lurch from crisis to crisis. This will bring a debate over the future of fiat currency into the mainstream, after which things will get very messy and political. (You can't run a welfare state on gold or bitcoin, for one).