For someone as familiar with the right and its fringes I'm surprised you're surprised. The 13th-14th-15th Amendment thing has been a bone of contention since at least Mike Beach, largely founded the 'Christian Constitutionalist' movement with his Blue Book in the 1960s. Paul earns double or triple points on the Civil War thing because it plays to the fringe whackos who claim that anything post-Civil War is "unconstitutional", to the mainstream racists and to the pseudo-erudite types who point to the 13-14-15 combo as being significant in the development of corporate personhood rights more so than outlawing slavery. All three of those groups have some significant overlap.
But it's also just stupid and hateful, but not surprising.
And it puts Paul as the definer of the fringe conversation. He's the nut, so when Gingrich does some fake-ass backpedalling on what he 'really' meant when he said that stuff about Barry O. as the "Food Stamp President" or when he (Gingrich) said that kids at troubled schools should work as janitors, it looks positively tame and a lot less complicated when compared to the Pauline Exegesis.
-- Nathan