I'm more cynical. I think most people really are intolerant. They have their culture which they perhaps unconsciously equate with being good or morally right and anyone who doesn't follow the complex unwritten rules is shunned or abused. Those rules may be mostly good but nobody questions them all, yet almost everybody either enforces them or tacitly tolerates their friends enforcing them. This is probably necessary because if everyone went around inventing their own standards for behavior, people wouldn't get along very well and the outcome of "most people get along with each other most of the time" is itself valuable - it just comes at the cost of those who can't understand it. I think most people can't comprehend the possibility that somebody who seems reasonably normal and intelligent doesn't understand the rules so they must be acting maliciously and deserve punishment.