Merely doing that is ethically neutral--often, in fact, beneficial. A clever hoarder will buy when prices are low (which is a source of price support for suppliers who would otherwise be suffering) and then sell when prices are high (providing supplies when there would otherwise be a shortage). If he makes a profit, it's a legitimate return on the capital that was tied up during a period of low prices. Buying low and selling high is not just a way to make money, it also helps stabilize the market, protecting both suppliers and consumers.