Next, Sowell moves on in A Conflict of Visions: Ideological Origins of Political Struggles to characterize how weak theories can get a life of their own under the unconstrained vision:
... In short, ideas originating in one vision may be adapted to another. But, for the Malthusian population theory to last long enough for this to happen, it first had to survive more than a century of contradictory evidence. Its success in doing so suggests that evasions and tautological formulations may protect a theory against evidence as effectively as outright falsification. [pg. 229]
... Theories may persist because the difficult task of bringing them to confrontation with evidence has simply not been performed with sufficient skill and care. This may be especially so when the person testing the theory has a different vision of his own, and reads the opposing vision in his terms, rather than in its own terms. [pg. 229-230]
A recent example of this phenomenon has been the oft-repeated assertion that higher rates of broken homes and teenage pregnancy among black Americans are a "legacy of slavery." Only after decades of widespread repetition of this assertion was a comprehensive factual study done-revealing that broken homes and teenage pregnancy were far less common among blacks under slavery and in the generations following emancipation than they are today. Again, the point is not that a particular conclusion was mistaken but that a sweeping and unsupported assertion went unchallenged for many years because if fit a particular vision. The ability to sustain assertions without any evidence is another sign of the strength and persistence of visions. [pg. 232]
The contemporary example of this is anthropogenic global warming: evidence that warming has stopped, and that supporters were in a panic about how to cover that up, hasn't changed the viewpoint of many ... because it fits into an unconstrained vision that only the best and the brightest can save us from ourselves. Poppcock!