What's funny is that even though my religion also states not to have strange gods before our Lord, or not to worship idols and such, we at least have enough sense to preserve history enough to learn something about it. We'll give people crap for worshipping them at the worst (and not all of us are dicks like that either; myself an example. If anything, we'd give more crap for celebrating Football like a religion (Keep holy the Sabbath Day; Church for at least an hour, not watching TV/[insert game here] instead), rather than worshipping another god), but even so, it's still history; we'd still like to learn something about other cultures. At least, those of us who are rational/tolerant (silent majority).
But overall, it's an extremist principle. Take something you believe in, and have so much faith in it that your rationality goes out the window. Just look at Westboro (vocal minority), and other religious groups that don't know how to draw a line in their beliefs. Even non-believers can be total assholes.
EDIT:
I guess, overall, certain people want a reason to be the very definition of the term "asshole" and get away with it, what better reason than "because God said so". I guess the amount of times that excuse has been made was what was so offensive to so many over the course of history.