Because it is hard to know where to draw the line. Some people get offended and some dont. We have to care about all.
I think all the arguments so far are ok and should be allowed. I strongly disagree with most people here. But the thread is clearly labeled and everyone knows what to expect in this topic. If you dont want to discuss religious views on this forum all other threads are safe to view. If you want to discuss it then you risk being offended.