Barry Goldwater supported every single Civil Rights Act placed in front of him during his time in the Senate. And he supported the original Senate version of the bill. However, between the original bill and what it had become over the course of the legislative process, it had changed. He had long supported Civil Rights, he simply felt that the newest version of that bill had gone to far, in taking away fundamental rights from states without a set time frame, and without any kind of easy system to get out from under them.
And remember, the "Deep South" has been among the most Conservative areas of the nation, even when it was held by the "good old boy" Democrats. During this time period however the Democrats made a huge fundamental shift in it's own policies. It went wildly Liberal, and most of the Conservative Democrats (I am talking the individuals, not the politicians) now found themselves at odds with the national party.
So given a choice between Lyndon Johnson (and his Great Society), it is natural that a lot went to other parties. Bluedog, Dixiecrat, the region started to split itself politically. The "Old Guard" continued to try and fight it out as Democrats, but found themselves loosing elections against younger Republicans with new ideas and without all the Segregation era baggage.
And this has only become more noticeable in the last decades. As the Democratic party becomes more and more Liberal, on the National level you find more and more Republicans in these offices. But interestingly enough, on the local levels, things are still either evenly split or more Democrat. Of course, a State Assembly person does not have to please a National Party, odds are the national party does not even know they exist.
This is why you get the interesting politics of a lot of states that are traditionally "Conservative". Idaho, Mississippi, Alabama, Utah, Arizona, states like these produce politicians that most of the nation really can't understand. Even Democrats from these areas normally come off as Conservative as Republicans in most other states. And when I moved from California to Alabama, I noticed just how odd this was. I seemed much more "Radical" then the majority of Democrats in the area. I remember trying to arrange a rally for Darfur, and everybody looked at me like I was nuts. And I was always looked at like I was this crazy California Hippie (complete with long hair and beard), who even as a "Conservative" was to radical for the local politicians.
Of course, I also admit the local politics were moderately corrupt, with "good ole' boys" who owned large areas of land in one area of town, so refused to grant any kinds of permits to revitalize another area of town, because it might negatively impact their land value.