Impractical, maybe, but not pointless. As someone else mentioned, insider trading creates perverse incentives for acting on undisclosed information, however, also some of those insiders have a possibility to directly influence those events, which make the perverse incentives even more perverse. Imagine a greedy CEO intentionally causing massive screwups and shorting his company's stocks, for example. At least afterwards it's much easier to prove insider trading than breach of fiduciary trust (also, the former is criminal, and the latter is civil.)
This is the primary concern of insider trading, and why insider trading laws don't exist for commodities markets (which are much less susceptible to willful manipulation).
Really? I have been under the assumption for many years the the commodities markets are thoroughly rigged. See for example (among many others) the Goldman aluminum warehousing case [0-1].
