How is a vote for someone else a vote for Obama? My vote never belonged to Romney; it never did. So you cannot even argue that mine is one less for him. To put it another way: if I do not vote for Romney it equals a vote for Obama, therefor not voting for Obama equals a vote for Romney. At worst, it is a wash.
Ross Perot got us Bill Clinton. Remember that? I do because I was stupid enough to vote for Perot. Never again.