Speculation about the (unknowable) future is how we allocate all resources in the present. A lot of people on HN seem to lump the "buy because price is rising" speculators in with the "buy because Bitcoin will become the foundation of the financial internet" speculators.
Investors who understand Bitcoin's potential do it an indispensable service. They inform the public (through price information) of that which most of the public is unable or unwilling to figure out on their own: that Bitcoin has tremendous potential to change the world and warrants serious attention, both currently for certain people as a hideable, unconfiscateable, transportable, no-third-party-risk store of wealth and in the future for everyone as a transactional currency (and as the cornerstone of the financial internet).