Nice strawman. It was you who claimed that this result showed the republican party was racist. I can assure you that many democrats probably voted against that referendum.
Are you referring to registered Democrats, or people who actually vote Democrat? Because many "registered Democrats" vote Republican nearly 100% of the time. Just look at Oklahoma for proof of that.
That's only a fairly recent development. I believe the AL state leg. was D-controlled until 2010, and a lot of that Democratic strength came from Conservatives in the rural, very white Northern part of the state. Probably about 25%~30% of Democrats voted against interracial marriage.