High volatility has benefits for traders, stability for customers.

If you want to make money from trading, you need the prices to change often and by a good margin. Therefore if bitcoin becomes stable, trading gets less appealing.
On the other hand you need a stable value if you want mainstream bitcoin adoption. A small shop does not want to adopt bitcoin because his earning would be totally unpredictable and he needs to be sure that value persists. Therefore stable bitcoin benefits customers and businesses.

In the long run, when mining rewards drop and price becomes more and more stable, we will probably see a better adoption of the coin in the public.
This will take a few years though and I am not sure bitcoin will be the currency. In the current form, even with segwit etc., it simply takes too long for quick trades of the currency. If you use bitcoin as an intermediate currency for trades or conversions, sure, that will work. If you want to use bitcoin to pay for your groceries at the small shop around the corner, you need quicker verifications.