Suppose that a company knew it had a half billion in revenue coming in over the next 6 months and kept it secret.

And that the officers of the company were sitting on tons of nice cheap stock options.

And you, as a shareholder, knowing all the public information available, decide to sell your shares to the company in an "announced buyback".

And, the day after you sell, the company goes public with the info they have been sitting on and the stock goes through the roof and the officers all exercise their options. Would you feel that you had been treated fairly?

There can be no insider trading before material info is made public.