Building off what Nemo has said, Group A and Group B are at odds with one another because they believe different things, even if only slightly different. One thing I've noticed among Christian culture - there's a very strong tendancy to state this is the way things are about a given topic. They're looking for security. Rather than face the unknown and try to find out who God really is, they cling to the cookie-cutter beliefs that were given to them by their leaders. I realize that's a bit blunt and harsh, but that's my perception of the issue, and I have the advantage of understanding Christianity from the inside. That's why they persecute any dissent - dissent destabilizes the consensus that everyone else has achieved. It's difficult to be okay with not knowing everything, to admit there are holes in our knowledge. It's much easier to intimidate and attack one who would point out such gaps.
