Sure, some people will invest in Bitcoins, and other people will invest in racehorses. (I avoid the problem by mining Dogecoins, which are almost totally worthless.) That's missing the point of Bitcoin, which is that it's intended to be a currency for relatively-private transactions.
Unfortunately, the markets that most wanted a currency for relatively-private transactions didn't do as good a job as they should have about being relatively-private on their own end (i.e. Silk Road got busted), but there is still a market for legitimate transactions, as you've pointed out.