I have no problem delivering a comprehensive answer based on a sound aprioristic analysis of how rigging markets distorts the basis of economic calculation and why a properly functioning gold market is central to all other financial prices. The difficulty is in answering the question in terms the listeners understand, bearing in mind I was told to assume they have very little comprehension of finance or economics.
I did not as they say, want to go there. But it behoves those of us who argue the economics of sound money to try to make the answer as intelligible as possible without sounding like a committed capitalist and a conspiracy theorist to boot, so here goes.
Manipulating the price of gold ultimately destabilises the financial system because it is the highest form of money. This is why nearly all central banks retain a holding. The fact we don't use it as money in our daily business does not invalidate its status. Rather, gold is subject to Gresham's Law, which famously states bad money drives out the good. We would rather pay for things in government-issue paper currency and hang on to gold for a rainy day.