If fiat would have been like this then I am pretty sure that economy of the whole world could have collapsed in matte of seconds. I mean fluctuations can cause the prices of stuff around us go crazy, we would have never put a price tag on the candy bar as we would not know whats the value of same currency next day with which we gonna buy it. Dont you think that this is the case.
Once bitcoin reaches or almost reaches the cap and mining no longer makes sense in a profit sense, I think the volatility will either die down completely or almost completely... After that point, bitcoin will go up or down in linear fashions long term.