Who knows why so many people thought MS was telling the truth, but this article in the Vancouver Sun from May 25th, 2016, might explain some of it:
"....Antidepressants increase our sensitivity to the pain of others, but they also reduce our willingness to punish wrongdoers and increase our tolerance of injustice."
Also, most people think they are capable of thinking rationally, while in reality most people aren't. Only people with an active, working knowledge of the cognitive pitfalls that prevent humans from thinking critically could even hope to train themselves to avoid or confront those pitfalls. Confirmation bias is something that most people don't even realize exists, and even those who do are resistant to the idea that they passively relinquish control over their faculties, reducing perceived mental acumen to little more than an ego-stroking exercise. An article on ArsTechnica explains, "Humans tend to flatter themselves by thinking they have the capacity to perform elaborate feats of moral reasoning, deeply considering possible consequences before arriving at an ethical decision. The reality is somewhat less flattering; a number of studies suggest we make moral decisions quickly and with a heavy reliance on our emotional response. Any reasoning that takes place tends to involve after-the-fact attempts to rationalize our decision..."
Juries don't convict on reasonable doubt or lack thereof, they render their decisions based on their emotions.