You seem to be only considering the purchase of shares as opposed to the sale of them. Also, individuals in a position requiring fiduciary responsibility should not be permitted personal motive to intervene in any manner, it's destabilizing.
A wide open, no holds barred insider trading regime would be endless boom and bust with a very few profiting enormously and the market at large being completely wrecked. That is not in the interest of business or the society at large.
Do you see any problem with Chertoff being closely associated with the manufacturer of these controversial TSA security scanners? That represents a conflict of interest, and it is insider trading of a sort. It's not just a matter of "fairness," it's immoral precisely because it's fraudulent, and tantamount to stealing. It's malinvestment perpetrated for the individual gain of a few, foisted upon the entirety of the country, at a great cost in money, time and individual liberty.
Just read about how the Randlords in South Africa concentrated ownership of goldmining and diamond mining at the expense of those with small lucrative holdings. And, interestingly, it was done on the London stock exchange.