[Update: To clarify, where there is a strong reason for authority to be at the state level we tend to see this argued on the merits, without reference to state's rights. It is only where a policy has little to no merit, or where someone seems to believe a given issue isn't really a problem (like Medicaid or poverty relief) but feels the public is pressuring them to take a stance that we see devolution to the states proposed (as a non-solution, since devolution is really just buck passing unless tied to specific policies), that we really see state's rights or devolution advanced as a serious argument. So we see alcohol (mentioned specifically because I think the state's rights argument has a great deal of merit with regard to the legal drinking age, which should be congruent with the habits and beliefs of the people immediately impacted rather than the beliefs and values of people thousands of miles away, but to my knowledge this argument is not seriously advanced), tobacco, and the speed limit regulated at the state level based on the merits, but we see state's rights used to defend slavery or Indian removal or advanced as a solution to poverty by people with an appalling record on poverty relief. I may be wrong about this one, but after reading the argument being used time and time again to strip people of life, liberty, and any chance of happiness I feel it is bizarre the argument is still advanced given its terrible history and would really like to know the other side of the ledger so I can understand why it is still used.]
I mean this as a serious question. After reading about the 19th century I see state's rights used time and time again to justify the oppression of weak individuals by stronger groups and individuals within society. The worst instances are slavery, later segregation, and Indian removal. We see the poor oppressed, often killed, maimed, stripped of their property, dignity, and even humanity. States rights were used to justify opposition to any action by the Federal government (in many cases with the collusion of Federal officials, with men such as President Jackson likely encouraging these actions by the states) to mitigate these wrongs.
Now, I'm aware of the principled defense of state's rights, arising both from the Constitution and from quasi-natural rights arguments such as their closeness to the people.* But, I have a deep distrust regarding our ability to discern natural rights or to derive just policies from principle. We must always be aware of our own weakness and seek to determine from the consequences whether or not our principles are correct or if we are deceiving ourselves.
Even where states have acted in advance of the Federal government to protect individuals against oppression by others or by organized groups, such as with gay rights, these arguments are made on their merits rather than by recourse to states rights. I can think of many instances where states rights were used to provide a principled veneer to otherwise indefensible evil and exploitation, I can't think of any where states rights were actually used to advance individual rights in the face of oppression (my lack of knowledge does not mean such cases do not exist).
Given that we have more than 200 years of history, what are the empirical results of this particular idea? I have noted many particularly awful instances in which states rights has been used by powerful individuals and groups to oppress those weaker then themselves. What is the empirical evidence on the other side? When have state's rights successfully defended individuals from oppression, rather than providing a seemingly principled defense of powerful individual's and group's oppression of others different from or weaker than themselves?
* I tend to feel the argument that groups tend to cancel each other out as democracies increase in size as being stronger than the closer to the people argument. It seems to me that the smaller a government gets the more likely it is to be dominated by a few powerful voices that will impose their will on the government at large, leading to the oppression of individuals and often to imposed uniformity. Of course, this isn't a subject I have expertise on so this is simply an impression from a less than complete knowledge of the literature.