I'm not sure that the issue is ignorance of another religion per se. We are usually talking about three things here: Difference in culture (which can be more pronounced than religious affiliation), Difference in appearance, and frankly the fact that a lof of people just like to hate people different then themselves. It makes them feel good about themselves. And this just gives them a good excuse to openly express their desire to feel better than others by bashing them.
I once talked to a man that had been in prison for a few years, and we spoke about how child molesters/kidnappers/killers seemed to be slain in jail by the inmates. I thought it was an example of an odd code of ethics, he paused for a moment, shrugged, and said: no it was just an acceptable excuse to kill someone . . .
This being said iit certainly doesn't hurt to study other religions and cultures
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