The problem here is you don't know your history... especially if you think slavery was "dying out" in the U.S. around 1860 and that "sending to back to the states" improved things. We were one of the last nations to abolish slavery, I think only one latin american country had a later date of 1872 or so. Most of the european countries had abolished slavery by the 1830s, and they didn't do so by "sending it back to the states". Read up about "Bleeding Kansas" and you can see exactly what happened when the federal government tried to wash their hands of it in 1858 and take Stephen Douglas' advise to "let the state decide for themselves". Epic disaster.
But since you believe that "federalizing matters always makes them worse; no matter how noble the intent or good the cause", would you support the repeal of the 2nd amendment and "sending it back to the states" to determine for themselves whether or not the citizenry in those states are allowed to have guns? States rights, right?
???
Constitutional amendments are ratified by the states. Which means the states agree with them. Why would you remove an amendment, that was agreed on by the states, as an example of states rights?
If anything, that's an example of statism.