Two factors come into play re inclusion and any religious group (info from New Scientist magazine recently so I'm repeating it rather than understanding it):
a) Does the group have a very very clear idea what God thinks re inclusion.
b) Is the group very very comfortable in each others' company and thinks of each other more like a family than a group of like-minded acquaintances?
I will generalise. Clearly exceptions apply....
When they tested groups that were very comfy with each other AND only had a vague idea about God's mindset, they found that such groups were far more wildly hostile to anyone different to them than other groups.
The more people feel like they're with family, the more defensive they get about anyone who might threaten that family's sense of security. (e.g. in one test, they were far more likely to recommend waterboarding for terrorists after they had been asked to imagine a lovely friendly holiday with people they love).
And the more they are left to guess what God thinks of inclusion, the more their brains fill in the gap with "Hey, it turns out God hates/excludes the same people I do - wow, how great is that!"
Undeniable human psychology, it seems.
So churches that are comfy and vague are actually the most dangerous places for anyone different to try to join. It's the opposite of what people would expect, but it's true.
It needs really strong leadership to enforce inclusion on such a group.
That's why so many make it work, and those churches that thrive on vague leadership find themselves shrinking more and more and more, as their groups repel more and more people 'not like us'. Yet, to them, they seem really friendly so they can't figure it out.
Does that help?