The problem is that in the future there will be no intrinsic reason for Bitcoin to be the unit of currency used to conduct financial transactions using distributed blockchains. Alternative cryptocurrencies like Litecoin and Peercoin offer the same advantages over traditional means of transferring funds electronically. The fact that these currencies trade like pennies compared to Bitcoin indicates that the current BTC price has more to do with the perception that BTC is a store of value than it does with its actual technological merits. This value disparity can only be justified if BTC is essentially preordained to remain the world's dominant cryptocurrency.
This is a specious argument. There are other cryptocurrencies that COULD offer the same functionality, but without bitcoin's marketing, brand name, momentum, and established infrastructure in its miners and its holders. So then they don't really offer the same advantage after all. A currency 's value is not solely determined by its technology and features.