Well, I took the reference to slavery to be a historical reference to the GOP's roots, and an attempt to point out that when one takes away the social issues, you are left with a rootless party that cannot prosper.
The first time that comparison was made I agree with your assessment but since the social issue\slavery comparison was made six times it went in a different direction.
By repeating (six times) that Rand does not support social issues and comparing that to the GOP founding on the social issue of anti-salvery it is clear that the implication is that he is for slavery, therefore racist.