"You're either with us, or against us" appeals to an audience to join a ground swell of public opinion and activity because everybody else is joining. The "bandwagon" technique appeals to feelings of loyalty and nationalism, as well as the desire to be on the winning side. The technique tends to obscure the ethics of the activity at the expense of victory: better to belong to the winning side than be too concerned with the rightness of the means to achieve it.
The "4 out of 5 doctors recommend..." slogan uses both the bandwagon technique and the argument to authority to promote an action. (The two techniques are commonly found linked.) In psychographics terminology, the bandwagon technique appeals most strongly to the group called belongers, those who make decisions because that's what everyone else is doing.
In the post-9/11 world, public figures in the U.S. find it difficult to express even mild criticism of the Bush administration's foreign policies -- so powerful is the bandwagon mentality that seeks to assert that everyone must unite in the fight against terrorism, the axis of evil, the makers of weapons of mass destruction, and those against freedom.
Obscured in this powerful propaganda technique are the facts that, for example, the U.S. has more weapons of mass destruction than any other nation, and is the world's largest arms dealer.
As the "world's most powerful nation," the U.S. has tremendous bandwagon appeal. Factors relevant to the bandwagon technique may be the fear of losing or the threat of reprisals.