Here are four descriptive statements rejected by the Left for these two mutually reinforcing reasons.
1. People are not basically good.
Leftists tend to reject this because a) it is too painful to accept, and b) it undermines the leftist dogma that people do bad because of outside forces — poverty, capitalism, racism, etc.
2. Men and women are inherently different.
Leftists have rejected this idea because some of the differences are too emotionally upsetting to accept. Men are variety-driven by nature? Too upsetting. Women may have less yearning for, and ability in, math and engineering? Only a sexist like former Harvard president Lawrence Summers would say such a thing. Moreover, the belief that men and women are inherently different violates the Left's foundational principle of equality. Many liberals admit that they reject talk of male-female differences because it can easily lead to gender inequality.
3. Black males disproportionately commit violent crime in America.
Leftist reactions to this truly painful fact are to label one who notes it a racist and to decry American society as racist because there are more black males in prison than in college.
4. The United Nations is a moral wasteland.
Since before the U.N.'s founding in 1945, liberals placed much of their hope for a peaceful world in the United Nations. That the U.N. has turned out to be an abettor more than a preventer of violence is a fact that the Left finds too painful to acknowledge. And it violates the left-wing belief that nationalism is evil and internationalism is the solution.
It is generally believed that as people grow older. they reject much of the liberalism they believed in when they were young. This is true, and one reason is relevant here: As we get older, we tend to make peace with painful faits de la vie.