The amount of "stuff" -- things of value which we wish to obtain through economic transactions -- is not stable and has not been for quite some time; it has, rather, been expanding at a rapid pace (consider, for example, the number of profitable industries today producing durable goods which did not exist even a half-century ago).
This represents a problem: if the total amount of currency available for use in transactions does not maintain rough parity with the total amount of goods and services available to be exchanged in those transactions, then the imbalance will lead to wild price fluctuations.
Since this situation is isomorphic to inflation (the only difference is which side of the currency/goods equation harbors the imbalance), the magnitude of the fluctuations will be the same as in an equivalent inflationary situation.
Thus, your point would be a strong one if only you were arguing for gold as an investment (since, in an imbalance of the type described above, the market value of gold would increase). As an argument for gold as a currency, it holds no water and in fact tends to undermine that position. In the present age, gold simply cannot be the foundation of a stable currency.