Despite the warm glow of self-satisfaction that the liberal vision confers on liberals, ugly facts keep intruding to undermine that vision. Some liberals eventually jump ship and defect to conservatism when the facts keep piling up too high to ignore.
This takes time, of course, and in the meantime there is a never-ending supply of new young people to become charmed with the liberal vision and replace those who have become disenchanted with it.
Other liberals hang on to liberal ideas to the bitter end -- especially when the end is not that bitter for them personally, when they live insulated lives in academia, the courts, foundations and other places where there is no price for liberals to pay for being wrong, no matter how disastrous the consequences for others.
Still, facts are a danger to the vision. In recent times, those on the left have increasingly sought to suppress facts that go counter to the vision.
Research dealing with innate biological differences are of course anathema to those with the liberal-left vision. Even research that turns up cultural or other behavioral differences between groups is almost as great a danger.
Both kinds of research undermine the notion that there are "solutions" that government can impose to eliminate differences, gaps, disparities or "inequities" that liberalism claims to be able to eliminate.
Scientific research into differences in the way male and female brains function is denounced by radical feminists, who are calling for a ban on such research. No matter what the MRIs say, the radical feminists say all differences are due to "society."
Liberals have worked long and hard to get the very word "sex" replaced by "gender," since sex is an innate biological fact while gender is an arbitrary social designation, much as the French language assigns the female gender to the noun "plume" for pen.
It is a sign of how easy it is to stampede large sections of society that so many people now find it necessary to refer to gender instead of sex, even if they have not bothered to consider what the difference is or why they have changed what they say.
When it comes to racial and ethnic minorities, liberal politicians and judges can make it literally a federal case to give IQ tests to black children. Among the facts that we would never have known if some people did not find ways around this taboo is that black IQs have risen in recent times.
The greatest danger to the liberal vision are facts about the consequences of liberalism itself and the laws, policies, and ways of life that the left has spawned.