I really love your arguments and often agree with them. I agree that high volatility in itself is not a problem. However, you lack one important component -transaction fees
They are dropping (for the moment anyway) and probably will fall further once the Lightning Network is up and running. But remember in a rising market retailers will hold their bitcoins anyway. Those who can afford to will hodl in a falling market and those who cannot afford to will not accept bitcoins in the first place. Still, there will be merchants who will indeed incur fees as they panic and convert to fiat. In effect they will be day-trading.