States rights does have one key benefit, IMHO, and that is that it allows for large-scale economic/legal/sociological experiments to take place in real-world conditions. You get great data.
The problems, however, often outweigh the benefits. Looking at something less controversial than the right to support bigotry-gun rights- states rights have resulted in an inconsistent patchwork quilt of State laws governing a fundamental constitutional right. My gun-toting buddies often lament that they can break serious laws merely by traveling cross country with a gun in the car because of where and how they have them secured. (Remember that when someone brings up the "shall not be abridged" language of that Ammendment.)
Similarly, the insistence that States should license health care professionals & insurance leads to increased costs of licensure & insurance, decreased mobility of health care professionals, higher mortality rates due to malpractice, inconsistent levels of healthcare or even what appropriate standards of treatment should be.
Why should States control educational standards? Historical facts are historical facts, math is math, biology is biology wherever you live. Leaving it to the locals gives us things like ID being taught in Louisiana science classes (thank you, bio major & Rhodes scholar Bobby Jindal), or schoolbooks in Texas that teach that we ended the Korean War by dropping atomic bombs. Or, back to the point of this thread, books that teach that the Civil War was not fundamentally predicated by the South's expressed desire to keep AND spread the institution of slavery.