Naturally a society which practices abortion but not abandonment would think so. But in both cases the function is essentially to provide a mechanism for infanticide to a society in which infanticide is prohibited (or rather, abhorred). There is a rationalization (for us, that the fetus isn't a child; for them, that the child is not actually killed, its life being turned over to the gods or to fate) but the rationalization is secondary to the fact that the act leaves the parent within, or on the border of, the normal workings of society instead of outside them altogether.