Ilya Somin, over at Volokh challenges the notion that unity - as proposed by Obama - is a good idea.
One of Barack Obama's major campaign themes is the promise that he will "unite" America. Obama is an incredibly skillfull campaigner, so I must assume that he wouldn't be pushing this trope unless there were good reason to believe that it works. Of course, Obama is far from the only politician to promise unity. Remember when George W. Bush promised that he would be a "uniter, not a divider"? That was a fairly successful campaign theme too.
This emphasis on unity for its own sake seems misplaced. After all, unity is really valuable only if we are united in doing the right thing. Being united in doing the wrong thing is surely worse than being divided, if only because division reduces the likelihood of the harmful policies being enacted. And even if the policies proposed by the would-be "uniter" really are beneficial, it's not clear why broad unity in support of them is preferable to just having enough votes to get them passed.
I'll suggest that this is a flat misreading of what Obama is saying, and what I think people respond to when Obama speaks of unity.
Simply put, the notion I believe Obama is expressing is that we live in a polity - that we share a common political space, rather than a loosely-affiliated set of allied interest groups. I think that the unity that he's discussing isn't a unity that suggests common action - marching in step - but the notion that we're all a part of the same parade.
One trend in modern politics is the relative decline of the nation-state, as smaller communities of interest and transnational bureaucracies, corporations, and religious and ethnic movements become more powerful in their claims to our loyalty.
That's a dangerous and frightening trend, and one that I believe presents greater risks for the kind of republic that we represent; because we are not a 'people' like the French, our attachment to each other is through our shared belief in that common political space and common political project - of liberty, of rights, of equality before the law.
I'd suggest that what people are responding to when Obama speaks of 'unity' - what I'm responding to - is his explicit recognition of, and promotion of the simple claim that we're all in the same boat.