Because I am a conservative and a Christian, I have had several people accuse me of being brainwashed, unable to think for myself, and one who simply spouts whatever I am told (like there is some guy standing over my shoulder telling me what religious or conservative things to say).
I think it is quite the opposite. I think that many of those with liberal leanings are the ones who are the ones who are, in many cases (not all), brainwashed. It has already been shown that the majority of the televised news media has a liberal slant, so, it would make sense that is how many people would lean in their thinking. It is more of a matter of, they hear a point of view so often, that they just believe it, without questioning it.
For an example of this, let me offer evolution. I suspect that almost every person here believes in evolution (or a creation by God wherein God used evolution). This is not because you have studied the evidence but because you have heard it again and again and again from a very young age, so you simply believe it.