This argument is a perfect example that just blindly following a single party is not good for democracy.
Unfortunately most people are lazy and will just go with one of the two parties and assume/pretend that that party either is completely aligned with them, or even worse, will adopt the same position on a given issue as their party since the "other guys" have taken the opposite position (i.e. "I don't care about about X but since my party is for it and the other guys are against it I will be for it.")
We have to look at each politician as an individual - not as a Rep/Dem/Indp - with their own stands on the various issues we care about. Unfortunately there is usually just one or two issues (abortion/Iraq/death penalty/etc.) which decide our entire opinion on that one politician.