That doesn't strike me as a very useful explanation here. Shame has long been a part of American discourse. For example, you could look at the attitude toward divorce. At the beginning of the 20th century, it was hugely shameful to get divorced. In the 1960s and 1970s, the divorce rate spiked to something like 5x the earlier rate.
Was that because outraged moralist scolds just pushed marriage too hard, ending the use of shame generally? Not at all. The rising legal freedom and economic prosperity of women, a change that had been ongoing since the suffragettes, finally allowed women to survive on their own. A measure of independence from the shamers was what made the difference. But at the same time, the Moral Majority increased their social power. The use of shame certainly continued.
For example, a lot of the post-Nixon reforms were built on shared moral standards and shame. An obvious example is presidential candidates publishing their tax returns. It was never a law, but it would have been shameful for a person wanting to run the government to conceal their financial interests.
Even now you still see shame being effective. Trump uses it extensively on the right, for example. Today he's trying to shame a governor into quitting. And as Campbell and Manning would surely agree, it's still effective on the left, even if it takes very different targets than it would have in 1950.
I think what's changed is not the amount or effectiveness of the shame, but changes in who people feel accountable to. Political polarization is one part of that. Rising inequality [1] is another; the 2008 financial crisis made it clear that the ultra-rich were basically unaccountable no matter the damage they caused.
And a big one comes from technology. At least from the age of Hearst through the 1990s, getting heard on a national scale required a fair bit of capital. Newspapers, magazines, radio, TV: all of them required significant, long-lived organizations. And the bigger the audience, the more capital was at stake. That drove a sort of natural centrism. But between cable and dropping production costs, that changed. The 1990s saw the introduction of reality TV, which eventually gave us both Trump and Paris Hilton. The Internet drove that further.
Now that the capital required to be heard on a national scale is approximately $0, it's very easy for people to build niche audiences. And with a sufficiently large niche audience, there's little material incentive to care what other people think. Now anybody can be a reality TV star all on their own, just as long as they keep getting people to smash that like button. In that light, we can look at Trump as the first influencer president.
[1] https://datatrekresearch.com/us-income-inequality-latest-dat...