Except that it isn't and never has been a 'two part balancing equation'. There is ALWAYS a null vote - Hell, something like half the country doesn't vote and never will. So it is at least a three part system by it's very nature (more than that with 3rd parties).
Is it your contention that every democrat that stays home is a vote for the republican? What about the independents? what if they stay home? who does their null vote automatically rack up for/against? Give the Christian Right something to vote for and their ranks can easily double, from 30m guaranteed to somewhere north of 60m... Obviously those are null votes becoming active and adding into the equation and not votes taken away from the 'other side'.
Your entire premise is without merit, and works against the will of the founders. Your vote is supposed to be a conscious choice *for* what best matches your beliefs... So quite logically, your vote *for* Romney is the same thing as a vote for Obama (because they both stand for liberalism/communism/globalism), and is a vote against Conservatism. There is the truth of it.
"Impress upon children the truth that the exercise of the elective franchise is a social duty of as solemn a nature as man can be called to perform; that a man may not innocently trifle with his vote; that every elector is a trustee as well for others as himself and that every measure he supports has an important bearing on the interests of others as well as on his own. "-- Daniel Webster