The truth is, we've always had reason to question the idea that cholesterol is an agent of disease. Indeed, what the Framingham researchers meant in 1977 when they described LDL cholesterol as a "marginal risk factor" is that a large proportion of people who suffer heart attacks have relatively low LDL cholesterol.
So how did we come to believe strongly that LDL cholesterol is so bad for us? It was partly due to the observation that eating saturated fat raises LDL cholesterol, and we've assumed that saturated fat is bad for us. This logic is circular, though: saturated fat is bad because it raises LDL cholesterol, and LDL cholesterol is bad because it is the thing that saturated fat raises. In clinical trials, researchers have been unable to generate compelling evidence that saturated fat in the diet causes heart disease.