I think the difference is that the extreme extremist JW's, Amish, Mormon etc don't subscribe to honor killings as an effective deterrant/punishment to speaking out or acting out against the tenets of their faith. They shun. At least for now, that's the limit of the extreme. Talk to a woman who wears the hijab or niqab or burka and ask them what would happen if they fall in love with a man who's not a Muslim. That boy had better convert to Islam and be damn convincing about it or it can get pretty ugly pretty fast. Which is why you don't see women who wear the hijab or niqab or burka going anywhere near men who aren't Muslim.
Ladies, please. Let's not in any way say that this is acceptable in the 21st century. Yes, the Christian religions have been through similar episodes in their history and yes, I think they're all crap but some crap is just way stinkier than other crap.