Heard the same rationale during the tech bubble. Bitcon is growing due to speculation, pure and simple. Those who got in early have ridden the bubble up, hopefully exiting before the burst, what you have now are all the fool lemmings following in their footsteps trying to make an easy buck only to watch their profits go bye bye.
But there are some enduring technologies as well as notable companies that came from the tech boom.
I believe that the same can be said for Bitcoin. Even if Bitcoin itself does not make it, the idea of a P2P currency concept like BitCoin is probably going to impact the world in significant ways that we cannot predict at present.
Also aspects of Bitcoin may fail while others survive and become more robust (certain exchanges, certain business ventures, client software, etc).
And the systemic risk argument has been beaten to death. The BitCoin block-chain has never been compromised.
Regarding making a quick buck by mining and speculation that was probably a necessary side effect of the design such that there would be a way to provide value for growing the btc base. That is simply brilliant.
IMHO the biggest risk is a lack of acceptance for BTC in trade vs some type of systemic technological risk.