If I were too apply the same standards of right to offense taking to myself I would have to briefly consider, the much worse fact that myself and other (atheists) are proclaimed to be destined for eternal hellfire by the most dominant religion of the west - Christianity. Hell is mentioned 23 times in the new testament, it's not an optional belief or an obscure interpretation. It's one of the most mainstream contentions found in the texts themselves. I struggle to think of anything more demented, disturbing and ghastly than the idea that you would torture someone, for eternity no less, for their religious belief. Yet this is naturalized to such an extent, that you seldom even hear anyone complaining about it. I even had a professor who when I raised this objection replied "well what's problem for you, you don't actually believe in hell anyway?".
On the grounds that it offends my religious beliefs I could, judging from the responses in this thread, demand that all religion be banned from schools, less I take umbrage. Better yet if I started some violence to stir things up a little bit. I would have droves of people cowering, demanding that the next time someone should have the audacity to mention religion in school, they should think twice of it, or they run the risk of riling me up even more. Go militant, get respect. Presumably, people would be defending me because I'm a minority (and one of the most persecuted minorities in the history of humankind), and because I'm protesting something that's genuinely disturbing and injurious. This is the equivalent of what I could legitimately demand, if I were to extend the logic of prevention of offense taking to my particular beliefs. It would only be fair that all mentions of the new testament be prohibited. Not that I am not obliged to read it, but that others shouldn't red it either. If this is a far fetched analogy, I'm waiting to hear which parts of it are not pertinent.
I think someone claiming I'm going to hell is much more insulting than most things that are deemed unacceptable by today's standards, and yet that one, hidden in plain sight, doesn't get half the attention.
Of course you can find the bible offensive in enumerable ways, and that's just one of them. Feminists can demand prohibition of texts on the grounds that god explicitly designates a subordinated role to the first female in the old testament. That's about as offensive to women as it gets, and you don't have to look for it it in the edge of a remark or anything. Perhaps they too need to get violent about this to have their cause defended vigorously by many a chivalrous knight on the internet, saying that teacher should have really known better than to cause offense by mentioning the old testament so irresponsibly.
None of these causes are (and I'd wager ever would be) defended in the same way, for the very simple and craven reason, that not showing approval doesn't carry the same palpable sense of danger and threat like the one in this instance.