Furthermore, if you actually believe that abortion=murder, then you wouldn't care about a religious exception, as it is well understood that we don't allow a religious exemption to allow murder, even if a religion had a sincerely held religious belief for child sacrifice.
As for the argument that abortion is worse than other things since it affects a 3rd party, why should the government allow a religious exception if it means killing a 3rd party who possibly doesn't share those religious beliefs? We would never allow a religious exception to anything else if it meant harming a 3rd party.
Bottom line, I don't know of a way to craft a logical and consistent argument to simultaneously say that abortion should be so heavily restricted because it is murder, but that there should be religious exceptions in some cases.