The volatility is the beauty of bitcoin, if bitcoin was not volatile it would have just existed like fiat. The volatility is what create the ability of people to make profit which is the main point of attraction, Though the main ideology was for decentralization of money globally.
In my opinion, you are mistaken. If Bitcoin was not volatile it still isn't the same as fiat. This is because fiat is managed by centralized authorities while one can have their Bitcoin to their self. At least, you are sure that the money will be fully under your own control.
The volatility of Bitcoin makes it very interesting to trade because there will be constant participants entering the market every single seconds knowing that the market must surely move will great activities. The Bitcoin market can never be compared to Fiat with so many differences that segregate them.
✓ Fiat is controlled by government while Bitcoin is not.
✓ Fiat is stable with tiny movement in price while Bitcoin is versatile.
✓ Fiat can not be used as an asset purposes because it doesn't appreciate in price compared to Bitcoin.
✓ETC.