Asbestos, lead paint, cigarettes, heroin(perscribed generously for basically whatever the doc felt like), "Radithor" (patent medicine containing radium-226 and 228, marketed as a "perpetual sunshine" energy tonic and cure for over 150 diseases), bloodletting, mercury treatments for syphilis, tobacco smoke enemas (yep that was a real thing), milk-based blood transfusions.
Didn't understand those either and used the fuck out of them because "the experts" said we should.
Smoking cigarettes didn’t really matter for as long as we were regularly burning wood for fuel. Turns out just burning pretty much anything and breathing in the particles is really bad for you. Makes sense we didn’t realize it was bad until we stopped burning logs and coal for home heating and cooking.
This is why I believe we should only listen to amateur opinions on everything, experts simply lack historical credibility. For example I've recently purchased a healing crystal (half off) for only $5000 dollars! It cleared up the imbalanced energies my street guru told me about right away.
I would never have been made aware about the consequences of imbalanced energies in the first place if I had asked an expert instead. They probably wouldn't even suggest an immediate solution to the problem like my reliable street guru always does! Something to consider.