Has that changed in the last few centuries? Have we so mindf**ked ourselves with advertising and propaganda that people are split down the middle, a "Belief Barrier" where it doesn't matter what the information is, half of people will never believe it? Maybe call it "Catch 50/50"
This could take a while. Another interesting paper that looks at other papers also points out it can be hard to compare the data from different studies, even beyond varying scales like 0-7, 0-10, or -50/+50. What type of & how questions were asked makes it hard to see the mean has changed over time.