When you look at near-history serial killers - ie the famous cases of the 50s-80s, you often find the phrase 'unwanted child' who was neglected/abused by a mother that didn't want the child, often born as a consequence of sex work. In some cases the child was abandoned and sent a broken care system that brought them up with a traumatic childhood.
Legalise abortion and the number of those children brought up with such a defining childhood fall, not completely, but statistically serial killers are rare anyway.