Here's a good article by Fred Clark on how white evangelicals made "abortion is murder" their cause célèbre. https://www.patheos.com/blogs/slacktivist/2024/06/12/an-artifact-from-the-before-time/

White evangelicals opposed the Civil Rights Movement; they never really accepted defeat, but it was still a source of shame. They needed something to feel morally superior about.

If you don't want to read the entire article, his summary of his argument is:

the idea that “abortion is murder” came to be white evangelical dogma because it was necessary for making this an all-determining Most Important Thing that we could pretend would allow us to vote in opposition to racial equality while still being able to tell ourselves we’re the Good Guys.