Southern Democrats were probably more pro-life than Democrats in, say, the NE. Also, at that time, Roman Catholics -- who were more pro-life than perhaps any other constituency, and perhaps still are -- were otherwise mostly supporters of the DP (think JFK). Abortion always was intended to be a divisive issue, to draw a line between "us" and "them", in order to indoctrinate budding feminazis.
I'd say, over time, abortion may be the one single issue with the most impact on the destruction of the DP, although other issues are also factors.
I'm not sure Southern democrats were more pro-life than NE Dems. At the time of Roe v. Wade, I think the Southern Baptists praised the decision. On the other hand, NE dems were largely Catholic or "Catholic." Even Teddy Kennedy was once nominally pro-life.