The most obvious reason why anyone would say "anyone but ______" is simply because that is the only person that they are fully conscious of, and that being said, they do not like that person. In my opinion, Clinton is probably one of the better politicians in American. In the eyes of the rest of the world, that makes her the most worthy of leadership. However, being the best politician does not imply all good things.
One of my sister's friends announced that she will be voting for Clinton purely to spite her extremely conservative friend. That kind of thing tends to be quite pervasive among uninterested college students.
I will say this. People get upset over small things all the time, and Clinton has not had the luxury of being out of the spotlight even for a moment since the scandal. Thus, every little thing gets blown out of proportion. Even so, our nation is founded on a certain principle that, if it is not upheld unconditionally by its leader, will ultimately humble our proud citizens. When I consider which candidate to support, I pray and ask God which will most honor Him and serve Him above all else. With that element, no lack of economic, political or any other knowledge will deter the leader because God grants a wisdom that surpasses any man may offer.