The role of cholesterol wasn't understood, saw a rise in heart disease and made the wrong connection, the food industry in the meantime saw a buck to be made..
animal fats and cholesterol are vital factors in the human diet, necessary for reproduction and normal growth, proper function of the brain and such.
Science keeps getting things wrong, people just blindly follow.
A couple of things:
1. "Science" is not one thing and scientific disciplines and good methods don't get things wrong. People get things wrong.
2. The studies and analysis that lead to the lipid hypothesis and conclusions was flawed. In part, many studies were poorly designed - that is the fault of researchers (people) incorrectly applying scientific methods to their research. In many studies of that era regarding this topic, their methods may not have been wrong but they asked the wrong questions (ie tested the wrong hypothesis). In some instances, it was just people misapplying their disciplines by doing everything to prove an hypothesis that they believed to be correct. That is an abuse of scientific methodology. Secondly, the analysis was often completely flawed. Conclusions were drawn that, had they been fairly scrutinised, would highlight total incompetence on the part of researchers (not understanding analytic methodologies, applying the wrong methodologies for the problem at hand, or willful abuse of the results to prove the outcome they may have been seeking).
All up, there was insufficient scrutiny at the time, which was scandalous.
No wonder people seem to believe that there were secret big food agendas going on at the time. I rather think that there may have been a stunning level of incompetence at the very least .. including the FDA in the US and similar bodies around the world.
Not much different to what happens now so often.
FFS everyone wants to be a freaking scientist these days and yet all the crap that is spouted as good science around the internet is mostly just crap, leaving most people with an even worse understanding of what constitutes scientific research.
Having said all that ... research is a continually evolving thing. Understanding of the world around us improves as our capability to study it improves - better methods, new discoveries, better technology.
So just because our understanding may change doesn't mean that the discoveries of the past were all crap because they were proven to be insufficient. Sometimes it's just that we didn't have the means to uncover what we can learn today. The same will apply in the future.
Our understanding of how cholesterol functions is a classic example of this.
The work of Professor Krauss in California (physicist) and his team has been a godsend for enabling medical researchers to investigate LDL and HDL and triglycerides much more comprehensively. This has helped turn our understanding of cholesterol and what is meant by "good" and "bad" on its head. the technologies they've developed and applied to the measurement of cholesterol particles did not exist before.