I don't think that's true. If you have a friend on the executive board of pharma company X, and he confides in you over the phone that the internal trials for the company's next big drug failed big time and they're going to announce the results to the public tomorrow, and you dump the stock... that's insider trading. It wasn't theft. The information was willingly given to you by an insider. And it's a crime because you made a trade based on non-public information, and the law has deemed that to be unfair and illegal.
The insider had no right to divulge that information. I don't care whether it's technically theft but it is definitely immoral, and should definitely be illegal.
If I'm busting my ass off in a startup I sure as heck don't want my buddy to sell or give away our trade secrets to the competition.
Also, think about the people on the other side of that trade. They're buying the stock being dumped based on public information, and you're taking advantage of their ignorance. Morally, that feels awfully close to stealing from them.
