No, you can be certain that if our Founders had intended to make slavery legal in every state, regardless of that state's own laws, they would have said so.
They did not.
Just the opposite, Founders recognized Congress's authority to allow slavery in some places while abolishing it in others.
Indeed, George Washington himself was obliged to obey the anti-slavery laws of Pennsylvania whenever he was in the US capital of Philadelphia.
So, as has unfortunately happened too often in US history, the Supreme Court's Dred Scott decision -- saying slaves could be kept in every state, and Africans could never be citizens -- that wrote new law, never intended by our Founders.
It's one significant cause of the 1850s Republican anti-slavery revolution.
DiogenesLamp: "It inevitably ends up being a situation where Northern states would be required to enforce slavery within their own borders.
Even George Washington drove a truck through that loophole."
But in fact, Washington obeyed the anti-slavery laws of Pennsylvania when he lived there.
Requiring all states to return freed slaves is them pretty much saying so.
Again, George Washington himself flaunted Pennsylvania's anti-slavery laws.
But seriously, tell me how this works. How do you get around "YOU WILL BE REQUIRED TO RETURN SLAVES TO THEIR MASTERS."
How does a "free state" get around that requirement?