It seems to me that the most important factor is not being mentioned here. That is money - who funds the research. Its a simple enough problem - eg if you wanted papers to show anything - eg 'that koalas cause forest fires in Australia' (I know that's ridiculous!) - then you simply fund a bunch of papers. If you have 10 papers, and 2 are supportive, 2 are against and the remaining are ambiguous - you have a start! Yo…
Also censorship. Opposite information are suppressed as unscientific, even through they are considered common knowledge. It is why it took 30 years for science to officially recognise asbestos and smoking as dangerous!