It might just be that the social sciences and medicine are really hard, and our best efforts fail often.
Edit: I mean the best effort we could reasonably make as a society, naturally there have been individuals and groups who have been doing things they knew or should have known were wrong for their own reasons.
As one field often builds upon another, the so-called soft/social sciences could also be called Higher/high-order sciences; and the complexity progression might not be linear, since at the high-level these topics tend to merge such that they are no longer layers but rather aspects of the same societal mega-graph e.g. economics is the study societal economy, political science is the study societal politics etc, all of which are part of the same system, and hence inter-react, in the same way a study of volcanic activity, the tides, the magnetic field, the atmosphere, weather and the terrestrial water table/system are all inter-related topics of the same planetary model (I expect all these things to become distinct topics of study too, at a greater scale if they aren't already).
Another consideration; Natural versus "human" sciences - any system that involves humans (any study of an aspect of human society) differs from the study of natural processes.
1) the scientists, or scientific institution is a part of society,
2) humans can react to scientific investigation and inquiry - a natural process doesn't do PR, no matter how strange the quantum is.
3) humans culture and behaviour is both complex, and changes over time in a way e.g. chemistry, does not.
We created frameworks for understanding political science and the humanities, still relevant today, millenia before any real neuroscience occurred.
It is true though that certain topics have been around so long that the study of X is itself a study.
I think the danger comes from people using results that aren't (can't?) be replicated and treating them as if they were fact.
"It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so."
And you're certainly right that we need to take into consideration how sure we can be about a result before relying on it, while recognizing that sometimes decisions have to be made based on the imperfect information available at the time.