Personal experience to me says a lot more than book reading. I could go into the theoretical reasons but all you need to do is to open your eyes to see this. The drawback of personal experience is that it is personal. It is not something you can communicate. It is like the problem that by its very nature perception is individual.
All one can do to support the point is point out the excommunication that the Gra signed but that does not seem to provide enough evidence for most people. One could also point out problems that got mixed up with it like the propensity towards bad character traits, but unless one has experienced this first hand he can always think the shiny public image they try to present is accurate,