Another great example of the insanity of religion. Judaism is inherited through the mom, but it's the same thing. Zoroastrianism is through the dad. I know some native American religious structures are also inherited through the mom. I don't know much about Buddhism or Hinduism. I can imagine that religions based on ancestor worship are anything but inherited. Interesting point, based on my incredibly limited knowledge, xtianity is one of the only religions that isn't also considered an ethnicity that you're born to. (In the US, again, must plead ignorance about much of the rest of the world).

Xtianity has been wildly sucessful, number of adhernats, number of other cultures it successfully destroyed. Maybe the lack of ethnic rules has helped it grow? On the other hand, islam is also wildy successful in the same way, but it has those rules about who your dad was. But I'm pretty sure you can convert to Islam just like Judiasm.... If you're not born into it, you can undergo certain rituals and be accepted as a convert. At least some sects... for instance, I think Shiites are much stricter than Sunnis. Kinda like orthodox vs conservative Jews. I'm running out of knowledge...

Side note: the Spanish Inquisition. I don't know the rules about how one gets to be catholic, but you definitely weren't allowed to become un-catholic. (You were "allowed" to die a catholic, so you wouldn't become uncatholic)

Kinda like baptizing an infant.