But apparently, those reasons just aren't good enough for Congress. So here's another reason, of which no one else seems to have thought:
If both the president and the vice president are removed from office, the next person in the order of succession is the speaker of the House of Representatives. The speaker of the House of Representatives is Nancy Pelosi. Nancy Pelosi is a woman. So then we have our first woman president, which means that we don't have to elect Hillary Clinton because we feel guilty about not voting for her, which means that we can vote for whoever we want in the 2008 election (unless, of course, we want to vote for Nancy Pelosi, in which case we're kind of out of luck).
(I hope that this will be taken in the satirical sense in which it was intended.)