I see three main reasons why the presidential dishonesty and anti-constitutional actions must be punished even if they are supposedly done in the intetrests of the country.
If there is no punishment, might they just do it again and again, for increasingly casual reasons, eventually destroying all trust in the president's role and allowing him to become a dictator?
If the president did this act for his country (eg. the Iran Contra Affair), maybe he's secretly doing more of the same for himself? (eg. the Watergate or Lewinski scandals)
Even if his actions serve the United States, it may damage other contries, seriously screwing up international relations.
Finally, many scandalous actions like Iran Contra and Extraordinary Rendition have _not_ necessariy been vindicated by history. Many people think acts like these did much more harm than good.
Here's one of those people :)
edited 4th Jan '12 4:11:42 AM by betaalpha