I suspect it has to do with what we identify with now. It's natural, almost a requirement, that we tend to assume who and what we are is good and true... and by extension the best thing for everyone. Granted, I don't have a formal framework that defines who I should feel sorry for, but because my early identity of exploring all beliefs came from my experiences in a narrow religious sub-culture, my reaction towards fixed beliefs is similar to any strong identity. Guess you could say that I feel sorry whenever someone believe they hold the one final truth in their hands. I probably would have the opposite (more in line with you) reaction had I embraced that lifestyle.