you are correct....but
There are plenty of scam artists out there for all investment options. The famous Ponzi Scheme was based on stock investments not the type of investments you are talking about.
The key is, if it sounds too good to be true, it probably is . As for metal investments, most diversified investors have some gold or gold stocks. If a real financial disaster ever comes all you say about metal values will no longer be true.
Always do your homework or find a professional that you can trust.