As someone who was living in the South at the time, I can tell you that the contemporary evangelical movement started with integration of the schools. To keep their children in segregated schools, white parents who could not afford existing private schools started using churches to establish private schools they could afford. Besides painting themselves as the only 'real' Americans, they immediately began searching for particular issues to use as fig leaves to cover their racism. Abortion is the one has that has best served their purposes.