There's your mistake. It isn't for spite - those who won't vote for Rudy actually believe they have the conservative movement's best interest at heart. If I vote for Rudy, I am voting for a guy who is anti-gun, pro-choice, pro-illegal, pro-gay agenda, etc.
You may see it as "beating Hillary", but the RNC and other liberal Republicans will see it as acceptance of liberal values, and will continue to push the party leftward. Rudy as president will help move the country leftward, as well - with no chance for repair until 2016.
I understand your argument - but your remedy is not justified by the risk