I see it, too. In my early-activist-ish days, back in university, some of the people I hung out with liked to call anyone who wasn't "revolutionary" "sheep" or "sheeple". I still see this cute nickname on the internets here and there, the implication that the majority are unthinking morons who need to have someone (like "us") tell them what to do, because otherwise they will never get it. An anti-vaccine person I know recently dismissed the entire medical and scientific community as "sheep" in a conversation I was having. Another queer activist that I was speaking with admitted that he doesn't bother communicating with a certain type of right-wing conservative because they never listen.
In a lot of ways, I get this. It's practical (and I think being practical - doing what works - is a good thing). Convincing one person who is dead set against you is nigh on impossible, takes a lot of resources, energy, skill, and is hardly ever successful. If you're dealing with issues that affect the world, it makes a lot more sense to focus on convincing the people who are sympathetic to your cause. You get more bang for your buck, and maybe, one day, you can reach a critical mass and social osmosis or magic or whatever will turn some of those who were dead set against you into people more sympathetic.
There's nothing wrong with that, but I think where we do go wrong is when we stop thinking of our opponents as people and start to see them as one big, unthinking blob. Zombies, sheep, theists, whatever. I think everyone does this to some degree, it's one of those time-saving patterns that our brains use to make walking around in the world something that is actually do-able. But I think that when we -do- do this sort of thing, we need to be aware of it and challenge it a little, at least for a couple of reasons.
The first is that dehumanizing is a great first step towards discrimination. It's effective, for sure. Look at any major pogrom or genocide in our history: a lot of effort goes into portraying the victim group as less-than-human. My pet theory is that doing this helps alleviate some of the cognitive dissonance involved in killing another human being...as social creatures, there's probably something in our make-up that encourages co-operation with one another, and that hurtle needs to be overcome before we go out and start senselessly bashing our fellow hominids without any real reason. I'm not saying "Republicans as zombies" leads to "kill the Republicans!!!!" but I think it's a part of the complex process that's involved in wiping out an other group of people.
The second is that it isn't true. People -aren't- sheep or zombies or whatever. It's impossible. The differences between us are almost inconsequential when you get down to it. There's some evidence that left-wing and right-wing people have brains that are wired differently, that they process information differently and react differently, but those differences are, in my opinion, beside the point. They're guideposts and clues as to HOW we should communicate, but they don't mean that we should stop communicating. When you dismiss someone as a sheep, you're dismissing the entire complexity that led to making them who they are...and when you dismiss them, you lose out on an opportunity.
As tempting as it is to do otherwise, we need to think of our opponents as people, at least once in a while. The reasons why I sit where I do on the political spectrum are many, but one of them is that I appreciate facts. I believe in an actual reality, and I think that if we are to do good, we are best served by acknowledging and acting within the rules we know to be true. If people are not sheep, they aren't zombies, then what do we gain by treating them like they are? At some point the flaws in our model will hurt our cause, especially if we use the model without any sort of reflection or acknowledgement that it is a model. People aren't zombies, they're people, and if we can't get a handle on that, we're just as wrong as "they" are.