I"m sorry, you still haven't pointed out any laws on this issue. Your references are to corporate and cultural hyperbole, which do sometimes have weight in a courtroom.

As to Yahoo or anyone else getting sued by shareholders, sure you can sue. The courts may take into account actions of corporate execs and decide they haven't been listening to the shareholders. But it really depends on what the shareholder rights are in any given corp. Was Yahoo required to put a buyout offer to a shareholder vote, but did not? If so, the shareholders have legal standing. But its not the reason you state: "exist for the sole purpose of advancing their shareholder's interest (profit). period. end of story."

In fact, I'll wager you cannot find such a clear law that supports your position.