I basically like your arguments and agree with them. I agree that high volatility is a non-issue in itself. Nevertheless you are missing one important aspect: transaction fees. They are low but whenever the volatility gets high, they get insanely high. And I think that the biggest issue currently is high transaction fees in times of large volatility and it is in fact a blocker for bitcoin being used as a currency.
Good point, but I think the Lightening Network should eventually resolve the fee problem, and as I understand it fees are already a lot lower than they were during the last feeding frenzy. Eventually SegWit will become the dominant address format, helping to keep fees under control. But also, if Bitcoin fees do go sky high, more and more people will be willing to use Ether or Bitcoin Cash or Litecoin instead. Excessive Bitcoin fees will eventually go away completely because fewer and fewer people will be willing to pay them and will know how not to.