Essentially this is historically unfounded. Nixon made the decision to go off the gold standard to prevent a financial crisis caused by Germany and other European countries leaving the Bretton-Woods system, in which other currencies were pegged to dollars, and dollars were pegged to gold. As the US began to run trade and budget deficits in the late 1960s, this system became unstable. Leaving the gold standard was more politically palatable than any other choice Nixon could have made in 1971.

As a matter of economics (but not necessarily the actual historical reason the decision was made) it IS a disadvantage of metallic currency (as opposed to fiat currency) that gold producing countries can effectively cause immediate deflation or a financial crisis by ceasing gold production. These concerns are for the most part academic amonst monetary economists, without being something that has actually happened. The are widely held by economists though, and the current economic embargo against Russia as a result of the Ukraine crisis would be less tenable if it produced a world wide deflationary shock.