States rights is evolving into a very low-leverage issue sociologically. The US, as a supremely integrated society, can't afford to have it's massive diversity of culture, devolve into city states with separate ideologies.
It's not actually ok that the south is slightly more racist than the coasts. It's not actually ok to leave gay marriage up to the states. For the 14th amendment to not be undercut, baselines for equality must constantly be working higher and higher nationwide, or we cease to have unified principles as a nation.