> per-capita income has more than doubled since 1972
Actually, per capita income has plummeted since 1972. To correctly assess income, you have to know the rate of inflation, and the official inflation figures are effectively lies because they focus on consumer goods, which have indeed become cheaper, while ignoring housing (and in America, college fees and health insurance), which has become drastically more expensive thanks to artificial scarcity created by zoning laws combined with the shortage of remote or rural jobs.
That sounds like only one factor of many, but I think it accounts for much of the rest. Real income falling every decade creates negative anticipation which has difficulty finding something to latch onto because we keep being told we are getting continually richer, hence the miasma of fear and hate constantly looking for targets. Nor is the fear unfounded. For centuries, we tried to figure out what destroyed the Roman Empire. Answer: the Romans were not destroyed by any external force. They were wiped out by their own ruling class, via abuse of land ownership law.
As for what to do about it, my first suggestion would be to start voting single-issue on repeal of zoning laws.