Insider trading laws apply to tradable markets, not transactions in other markets.
In other words insider trading IS arbitrary in definition. There are lots of people who got very rich very quickly in other markets such as commodities (not commodities trading) and real estate on the very fact that they got the information first and exercised accordingly. As you've stated in your last paragraph, if the purpose of making insider trading is to create a level playing field (more on that later) why is it that trading is considered inequitable but not other markets where one can get rich just as fast?
Your analogy to a speeding airplane over a school zone is flawed. Driving laws won't regulate the speed and height of an airplane, but aviation law DOES have laws that regulate the speed and height of an airplan's flight. So there is no inequity created there because the overarching theme of both forms of transportation - safety and well-being of passengers, bystanders, and operator - are still intact. The same cannot be said of insider trading, where only the trader is subject to stricter scrutiny than some other investor.
As far as your example is concerned I still don't see the difference to what I've pointed out, serendipitous or not. In your example above, you've defined the public as only being released to other traders. How does that apply if, in random conversation with another person, I mention something that is privileged information but the people I am conversing with are only privy to the knowledge that I work for the company? Has my unofficial release suddenly turned that information into public information? The case above says it did not, but then what happens if I have the same conversation but a third party unrelated to either me or my conversating partner hears it and then trades on the information? Is that person guilty of insider trading?
My point is that insider trading is being ever expanded so that the lines between what is or isn't illegal is becoming more blurred. The definition of insider trading, when it first was established by The Securities Act of 1933, was very limited in scope and really only applied to executive leadership. Now, after case upon case being argued in the courts, the definition was been expanded to include almost anyone who has some tangential relationship to the information in question.
The problem that is created by insider trading is that it removes an equal playing field. The integrity of the market is harmed.
See this is the problem with the entire premise of insider trading. In what way did the above two, or Rengan Rajaratnam or Joseph Nacchio (who's a bastard for many reasons, but not for insider trading) create an inequitable playing field by trading on information they knew about? At least in Ol' boy Joe's case Qwest was going to sink either way and that was due to mismanagement and making a buy on an overpriced telecommunications company. In fact, and you can attest to it, but the stock market is inherently inequitable. How exactly is it fair that venture capitalists and hedge funds can get in on the ground floor of an IPO and drive the initial price to astronomicl proportions before even the stock has officially been released?
Again, with your SAT example, the cheater must purposely steal information in order to get ahead. If insider trading was solely regulating the illegal obtaining of a corporation's information for the purpose of financial gain I would be in lockstep with your thinking because the thief used ill-gotten means in order to enrich himself. But then we have laws against theft already so I wouldn't see the need for another law regulating theft.