Assuming that there won't be any economic crisis in the future is a wishful thinking. Sooner or later there will be crisis no matter who is manages/cnotrols money.
Financial asset prices go up and down naturally, people make mistakes about investing, and unexpected events happen. All these things can move asset prices pretty significantly. People win and lose, and if they're not forced to take risks by the monetary system, and they're reasonably sensible, they won't bet the farm on anything. (If money's value was stable, they would probably do nothing with most of their savings.)
Major bubbles, however, requires some sort of fragility, and the biggest type of fragility happens when the state artificially props up the value of something, directly or indirectly. The fundamental reason the state can and wants to do this (wants to because it wants to create demand for its money and debt) is that the state runs money.
People who live in the modern period have seen so many financial crises around the world that they think crises are inevitable. This is because money has been managed by the state, and/or by the dominant world power, since the founding of the Dutch and English central banks in the 16th and 17th centuries.