No, insider trading in the U.S. Congress is never justified, because the Congressmen are entrusted with the public's confidence. Congressmen should be held to a higher level. Congressmen should be allowed to know even less than the educated public does. Congressman usually end office rich, and it's scary to think of how they got that way, earning modest salaries.
Congress has decided that, for almost everyone in the United States, trading on so-called inside information is a crime punishable by massive fines and imprisonment. These laws, however, do not apply to members of congress or their staffs, notwithstanding the fact that congress more often than not knows how proposed laws will affect companies' stock prices.