The question every human must ask is "who labelled him/her as muslim, catholic or jew?"was he born with a label on his body? are new born babies born with labels identifying their religion?
well, this is a very easy one. Since conversion is not the norm, the answer is: the parents. It's that easy.
One is born a muslim or christian or an atheist, and then in time, one may chose to re-define oneself or abandon the parental religion (unless that religion is Islam, in which case abandoning the faith could result in very serious injury).
If anyone had any doubts about the power of terrorism, just see where it forces otherwise sane, intelligent minds to go just to avoid the unpleasantness of the truth:
The 2nd question which every human must ask, who has made these -man-made-boundaries. Was the earth created with boundaries/lines? This is France. this is Argentina. this is Iraq? what if.. every human was born with wings like a bird?