Not my point, Unionist. I was referring to your phrase "sticking to their own and being xenophobic..." I'd rather not begin enumerating other groups that fall under this rubric. I was disputing your argument as much as saying it's not exclusive to religions. Hey, maybe I'll go out on a limb and suggest some religious people and maybe even religions are left-wing.
Do you know of any other organizations that discourage intermarriage with non-members of the organization? I happen to think that's a really important "negative" of Judaism, Islam, Catholicism... And in other contexts (like South African apartheid laws), it is universally reviled as being anti-human. But religion makes everything acceptable.