Actually, most ancient peoples of the classical world, with only a few exceptions, routinely practiced infanticide. The unique thing about the Spartans was that the decision was made by a committee of the State. In all other countries the decision was made by the head of the house.
The two exceptions I’m aware of were the Egyptians and the Jews. Historians and travel writers of the time routinely commented on these nations’ extremely odd customs. “They raise all their children. How very peculiar!”