I fault people to the extent of their malicious intent or their '7 deadly sins' but no further -- never for gullibility.

A child is born gullible and some people never grow out of that, some may not even have the mind to get beyond it, and some may mistakenly believe that innocence of worldview is as valuable as innocence of intent or action. Some may have burdens and scars too deep to take on any more emotional conflict, to accept the pain that comes with reshaping your mind in a way that conflicts with your upbringing.