We don't need federalism. The federal gov't were the ones that put a stop to the farce that was "Separate but Equal". They broke up the Trusts. They enabled the Unions that created the middle class. They bring in real and effective disaster relief and keep our shipping ports open.
The judicial body which struck down "seperate but equal" is the same one that made the Dred Scott decision. The federal government has committed Indian genocide. They've locked up Japanese in internment camps. They built Gitmo and secret offshore prisons. They've pushed No Child Left Behind, the drug war, Mccarthyism and any number of other bad policies.
Where the federal government has been successful is in implementing at a national level policies which have been proven effective and desirable in an increasing number of states. If you're only going to look at the tipping point then it's easy to blame the states which are still holding out as the enemies of progress. But what you're forgetting is that under a single national government the more progressive states would also have been prevented from being progressive up unto that point. Vermont ended slavery in 1777, and the other northern states by 1804. It would been an awful long time before there were any free blacks in the United States if it had to wait for nation-wide concurrence.
Look at Flint, Mi's Water supply (that Gov Snyder is still fighter the cleanup of) and the complete breakdown in Democracy it represented.
You're going cite one of the fifty states having a major problem as proof against federalism? So how many of the 43 presidents behaving badly do I need to cite in response? How does the Flint debacle compare with the EPA spill in Colorado?
Any government is prone to good and bad, whether at the state or national level. The advantage of a federalist system is compartmentalizing the bad while allowing the good to gradually increase its purchase. For that matter, if we had not been conferring so much power on the national government in recent years, the prospect of putting Trump in charge of it would be far less ominous.