[edit] In many political circles. In the antebellum era of US history it was used to excuse and defend slavery, and later, Jim Crow laws and segregation. There is a legitimate need for states to protect their rights, but that's not how the phrase has been used historically.
I am in favor of concentrating power in the hands of the people and have a bias towards local over regional or national. But I won't ignore the reality that many who have pushed for "state's rights" as a term were specifically fighting for the rights of states to oppress minorities. This is why I prefer to express my politics through phrases like "power to the people" and not "power to the states" - when states are undemocratic, they should have no rights.
Yeah, it's not like (for instance) the Constitution expressly forbade Congress (despite it's otherwise general power over international trade) from limiting the slave trade until 1808 except by imposing an import duty capped at $10/head.
Or like the Congress passed, and the federal executive enforced, and the federal courts applied laws protecting slaveholders rights over wayward property even if it strayed into free states.
Except, well...
Slavery was sanctioned at the federal level, protected by elements of the Constitution and defended by federal statute, up until after the Civil War.
Ever hear of the Fugitive Slave Act, the Dredd Scott decision,and the 3/5 compromise, among many other things?
Technically, the US is not a true democracy. Our state's speak for us and our state's represent us. This is how a presidential candidate can get less than a majority vote and still be president.
There is a term for it -- maybe republic -- but I'm not that awake and can't quite put my finger on it.
The current system creates incentives for states to split in two. What's the point of that? Why is it correct that Rhode Island and Connecticut are two states, and California is one state? It strikes me as an accident of history the number of states we have. It makes sense if states have a real choice about being in the union (as otherwise the small states wouldn't go for it) but without that, what do the big states get out of it?
Likewise the amended constitution limits the ability of the Congress to pass certain laws, without amending the constitution first.