That might have been true in 2002, but a few cherry-picked human interest stories do not accurately describe the state of our nation.
Every time a mass shooting occurs, we are greeted with anti-Christian bigotry mocking prayer, demands to seize guns, and consistent blame toward white men, toxic masculinity, etc. Those who do not agree with the prevailing dogma are having their livelihoods attacked. Is that a sign of a united nation? I think not!
Let me give another, broader example. Perhaps the best way we can look at personal relationships as a whole is through the lens of family. If men and women are still coming together at the same rate as they did before, then Tanner's hypothesis has some merit. But it's not. Age of first marriage is through the roof. Divorce rates, while down somewhat due to fewer marriages, are still sky-high. Birth rates are through the floor, and many of those that are born are out of wedlock. That is a perfect, measurable example of our country being pulled further and further apart on a personal level. Institutions, and our faith in them, are crumbling. Our communities are being pulled apart by a painfully inconsistent economy that benefits large cities but leaves large swaths of America in the dust.
We still have a few things in common, most glaringly our language. Most of us still speak English, for example. But let's not kid ourselves: the days of national unity are over.