For Christians, yes. It's their admission into to the church. To an atheist I imagine it's just a pointless ceremony.
JLM wanted the real reason so why make **** up or guess at things?
I can't speak for the other Christian dwnominations except for Catholic. For Catholics it's more than just being baptized into the Catholic faith for the child. The parents and the Godparents have a very large role. The Parents promise to bring the child up in the Catholic faith and the Godparents, who are the child's representatives or advocates promise to help and ensure the child is brought up on the faith if something happens to the parents. I know of no member of the clergy that still advocates that it is to absolve the child of original sin as Jesus Christ died on the cross to absolve all of mankinds sins, including the original sin.
I'm currently in the process of negotiating our soon-to-be child out of baptism (I'd rather let her choose) but the grand parents are definitely going to bring a fight.