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?
But nobody before the 1857 Dred Scott decision even imagined that Southern slave-holders could move permanently to Northern free-states and still hold their slaves in bondage.
The basic principle here is very simple: Northern states must respect Southern slave laws by returning runaway slaves.
Southerners must respect Northern anti-slavery laws by not bringing & settling their slaves in free-states.
That's the law which you claim Washington "flaunted".
In fact, Washington conscientiously followed the letter of Pennsylvania's anti-slavery laws by cycling his slaves in and out within the allowed time period.
So, our Founders' original intentions are clear here, and it is the Supreme Court's 7-2 Dred-Scott decision which was way, way out of bounds.