I did some reading on the ancients and infanticide, and the picture is murky—the Christians were not responsible for making infanticide illegal, that seems to have preceded them, but they claimed the laws were honored mostly in the breach, so whether you give any credit to them depends on your theories of causality, large-scale trends, and whether the Christians made any meaningful difference to the actual infanticide rate.
I did some reading on the ancients and infanticide, and the picture is murky—the Christians were not responsible for making infanticide illegal, that seems to have preceded them, but they claimed the laws were honored mostly in the breach, so whether you give any credit to them depends on your theories of causality, large-scale trends, and whether the Christians made any meaningful difference to the actual infanticide rate.