Research results in applied psychology often have a big impact on the general public because those works address questions that people can directly relate to. Who isn’t interested in what we are like and how we relate to others? Sometimes the research results cause great controversy and can even lead to rapid changes in public policy.
This article lists ten studies that the author asserts are the most controversial. Of course there is no way to objectively judge which are the most controversial and any such list is purely an opinion. But the title worked as clickbait with me and I looked at the list. I found that I was familiar with six of them (1,2,3,4,6,10), suggesting that the list was at least pretty good at identifying studies that received wide publicity. A good feature of the list is that it discusses both the claims and the counter-claims and provides links to both sides.
I am not sure whether the list is ordered in terms of importance or reverse importance or just random but I would say that #10 (the studies that suggest the absence of free will) are the most controversial because the idea of free-will is so engrained in our sense of self that to challenge it will cause many people to recoil.