people might have had more sympathy for States' Rights if states didn't use them to oppress people.
Civil rights has always been pioneered by the states. You probably remember the Emancipation Proclamation was issued by the federal government in 1863. But I am willing to bet you forgot that slavery was abolished in Rhode Island almost a hundred years earlier in 1774, Vermont in 1777, Pennsylvania is 1780, Massachusettes in 1781, New Hampshire in 1783, Connecticut in 1784, New York in 1799, and New Jersey in 1804.
Right now, who has passed DOMA, and who has legalized gay marriage? Who has legalized recreational marijuana, and who is sending agents to bust the dispensaries?
The simple fact is that any government is oppressive by definition, some worse than others. But the state system limits the total power of any of its oppressive elements, and reform can happen in one place, achieve meaningful results, and those results can spread elsewhere. At the very least, if you are in a state whose laws don't suit you, you can move to another state (even in an extraordinarily oppressive situation you wind up with things like the Underground Railroad). Relying on a central government does mean that states lagging behind the average are forced to catch up---I'm willing to bet that is the only part you think about when you consider central government vs. federal government---but it also means holding everyone back until that central government is ready to make the move. And which form do you think is more removed from the people it represents, and which has the resources and inertia to lay more heavily upon its citizens?
Everyone wants the federal government to swoop in and pass laws to get all the states on board with their latest agenda. What they forget is that if we actually had a system like that, they would still be occupied trying to undo the laws passed fifty years ago. (probably until they had enough votes to override a fillibuster)
Ostensibly, the same people who decided our nation was to be known as the United States of America.