What I take you to mean is that we all at some points think that some other group is united - but this, to me, seems a separate phenomenon from groupthink. If groupthink is the "levelling" of one's own opinion to gain greater social harmony within the group (not rocking the boat), then recognizing or misrecognizing a unity of opinion in some opposing group is "out-group homogeneity" (and actually has its own literature). No doubt this is also a concept of social psychology.
I also do not think either can be dispensed with. All groups seeking political office are imbued with the will to power (as are all humans) and so will necessarily need to appear as a united front against the enemy (who must be vanquished). Groupthink is needed to keep people toeing the party line, and outgroup homogeneity is needed to mobilize around a common enemy. To get rid of either is to aim for a unity of people in a bounded political society, and this is both impossible and ridiculous. Impossible because all social systems are riven by intense animosity of the "other," the "unlike," etc. Ridiculous because nobody is willing to cede to the enemy whom they think is oppressive or bad. If this seems pessimistic, then it is a helpful exercise to think about what you are willing to compromise to these more moderate Democrats who voted 3rd party, and if the answer is "nothing" or "not really all that much" or "none of the hot button issues that make the news" you've effectively proven my point (for this exercise I presume you to be at least somewhat conservative given what you said above, but the same works if you are a fascist, communist, liberal, anarchist, etc.).
In short, these not-quite-true depictions of a common enemy are needed to foster resentment and group belonging by demarcating between the acceptable and the non-acceptable. My favorite example of this is the somewhat subterranean exchange between Henry Jaffa and Allan Bloom on Bloom's sexuality. It is not explicitly evident that Jaffa is demarcating Bloom as an "other" (and we might not ever in fact know how much Jaffa's invocation of AIDS as God's "terrible retribution" for homosexuality and a welcome return to proper hatred, indeed, a "joke," is directed toward Bloom who was open about his homosexuality, though it was written in a review of Bloom's seminal work) but it is clear that he is sending a message to his brand of Straussian conservatives: be a homosexual at your own risk, and expect to be ostracized. The divided line ends here. Indeed, he vests this demarcation with theological veracity:
"Last spring I told a class of freshmen (and women) that there was a race on, between God and science, for their moral allegiance. And, I added, somewhat sententiously. that it would be very unwise for them ever to bet against God. A few years ago, this remark would have provoked gales of laughter. This time I looked out upon the most solemn faces I had ever seen! Thanks to AIDS then, we have a little breathing time to reassert the true arguments, the “enriching certitudes.”"
In a similar fashion, the populists are right to demarcate the friend and enemy distinction between the people on one side and the CEOs, empty suits of incredible varieties, and false moralists on the other. Such a distinction must be sustained by semi-false beliefs about what the other side is. Are all CEOs nihilistic and selfish? Maybe not. But this does not bear on the politics of group distinctions, nor does it matter for forming a political consciousness. All groups are essentially paranoid. All groups are essentially bound by a profound (if untrue) faith.
But what do I know? I'm just McDonalds.
-RealMcDonalds
