In some places you don't. If you live in, say, Florida, or Ohio,
and you abominate the Republican choice for president, then you
must vote Democratic. And conversely, if you can't stand
Hillary/Barack/John/whomever, you gotta vote Republican. Because
your vote, and the vote of other thinkers like you, could
possibly make a difference in who the state goes for.
But many of the rest of us don't suffer under this severe
necessity. If you live in Massachusetts, or New York, or
Maryland -- or if you live in Texas, or Idaho, or Tennessee --
you know how your state is going to vote. There is absolutely no
point in, say, Maryland, in voting Democratic, to swell the
majority by one more vote, or in voting Republican, to decrease
said majority by one. And the same argument goes for e.g. Texas,
except with the words Democratic and Republican interchanged.
How you use that vote depends on your individual leanings, and
your view of society. You might, I suppose, want to write in
"David Duke"; if five or so fellow inhabitants do so, it will
almost certainly get some press play. More rationally, you,
together with several thousand others, might wish to vote for the
Green Party candidate, or for the Libertarian Pary candidate.
Such a vote will encourage your fellow enthusiasts and, again,
if there are enough of you it will get some press play.
If you are totally cynical and want to flip the bird to the whole
system, you can write in your own name, or Mickey Mouse or
Superman, or whatever. This act will bring you a few fleeting
seconds of satisfaction, right?
But I think we can agree that any of these uses of your Free Vote
are more effective in expressing your choice than in making a
conventional Dem/Repub choice in a state where the outcome is
foreordained. (Of course, if the Dem candidate is X and the
Repub candidate is Y, and you totally love X or Y, then your
vote is clear; but equally clear is: you are in a tiny minority,
wherever you are. Imagine loving Hillary, or Mitt Romney!)
Why don't more people use their Free Vote? I conjecture that
the societal pressures to avoid this rational alternative are
simply too great for most people. For there are various issues
on which the Dems and Repubs differ; but one issue unites them
passionately. It is: that the Two-Party system is the only way
a democracy can function, that the Two-Party system is engraved
in the Constitution, that if the Two-Party system should break
down, it would be handing the country over to Osama bin Laden,
or Hitler, or whatever monster you fear most . . .
So watch it! if you proselytize for a Green or a Libertarian, or
for yourself, or Mickey Mouse, you will be viewed as a kook/wacko
by all your acquaintances, and by the Grave Voices of Sobriety
that exist almost everywhere. But pay them no mind; use your
Free Vote -- if you have it -- in whatever way suits you. If
enough of us free people use our Free Vote, perhaps the system
will become at least a little bit more free. And we can all
agree that that would be wonderful, right?