Two things to consider: First of all, as a totally new asset class we are probably still in the price discovery phase of Bitcoin. In 20-50 years we will have a much better understanding of the nature of cryptocurrencies economically and I'd bet the volatility at that time will be much less.

Second, it's possible there could be a mean-reverting effect such that the long term volatility is less than you'd expect by looking at the short term volatility. Some claim that gold has this property and it's possible that Bitcoin might as well (not really enough data yet to tell).