You are ignoring the US system, you don't need to vote for either.
If a candidate promises to implement or action something you strongly agree with, then there is motivation to get off your a and vote. And if the candidate turns out to be FOS and does not even attempt to make good with the promise, it is highly unlikely you would get of your a and vote for them a second time.
On the matter of lying, a liar is a liar, telling one more or less lie does not change your status as a liar.
