Since the indictment of Martha Stewart on "insider trading" brouhaha, there have been many angles of Stewart-defending in libertarian circles. Most are dead on, but there's one that is unnecessary and incorrect (though barely so).
Some state explicitly, others merely lean in the direction, that nobody could have been harmed when Stewart sold her ImClone Systems shares before word of the FDA bunglers' decision made the rounds. They say it was a "victimless" transaction. Theoretically, that's not true. Still the question is, as most reviewers rightly stress, "Who harmed who?" It's the person who bought Stewart's stock who harmed himself. It shouldn't be ignored though that there's a chance the buyer wouldn't have bought ImClone before the plummet if Stewart hadn't offered her shares for sale at the price and time she did.
In many discussions of stock transactions it's assumed that when a stock hits a certain number, the market for shares is wide open at that price. Of course that's not how it works though. Buyers must find sellers, and vice versa, sometimes even with an exact number of shares. Market equilibrium's price dances around, as anybody who watches stock streamers knows. What is possible now may not be so 30 seconds later. The buyer(s) of Stewart's shares may only have bought them because those particular shares were on the market right then. Perhaps it's not likely, but it's not something to dodge with untruth. It is possible that Stewart's sale did contribute to the environment in which a buyer harmed himself by not having the same information. A worthwhile counterpoint is that Stewart's sale could have helpful effects for others, but such nitpicking degenerates into territory that's impossible to analyze. Better to bypass all conjecture, or at most allow that somebody may have harmed himself because Stewart presented the opportunity with her better information.
It's then that the real libertarian argument steps in with, "Yeah? What of it?" That part, so closely resembling life's natural knocks, is what trips up the average socialist (i.e., typical modern American).