"The 1780 Act prohibited further importation of slaves into Pennsylvania, but it also respected the property rights of Pennsylvania slaveholders by not freeing slaves already held in the state. It changed the legal status of future children born to enslaved Pennsylvania mothers from "slave" to "indentured servant", but required those children to work for the mother's master until age 28. To verify that no additional slaves were imported, the Act created a registry of all slaves in the state. Slaveholders who failed to register their slaves annually, or who did it improperly, lost their slaves to manumission.
The 1780 Act specifically exempted members of the U.S. Congress and their personal slaves. Congress was then the only branch of the federal government under the Articles of Confederation, and met in Philadelphia.
1788 Amendment
An Amendment, created to explain and to close loopholes in the 1780 Act, was passed in the Pennsylvania legislature on 29 March 1788. The Amendment prohibited a Pennsylvania slaveholder from transporting a pregnant enslaved woman out-of-state so her child would be born enslaved; and from separating husbands from wives, and children from parents. It required a Pennsylvania slaveholder to register within six months the birth of a child to an enslaved mother. It prohibited all Pennsylvanians from participating in, building or equipping ships for, or providing material support to the slave trade.
The 1780 Act had allowed a non-resident slaveholder visiting Pennsylvania to hold slaves in the state for up to six months. But a loophole was soon identified and exploited: if the non-resident slaveholder took his slaves out of Pennsylvania before the 6-month deadline, it would void his slaves' residency. The 1788 Amendment prohibited this rotation of slaves in and out-of-state to subvert Pennsylvania law."
While their intentions were honorable, how is any of that constitutionally legal?
If a legislature can tell a slave owner how he must conform to the legislature's wishes as to how he should treat or move his slaves, then why don't they just tell him he can't have any in the first place?
What I'm saying is that if they can legally put conditions on it, then by the same principle, and by the same authority, they can legally ban it.
I think there is a dichotomy of principle between the opinions of the legislature and the mandates of the US Constitution. I think they are going beyond their legal authority, but as we have discovered innumerable times by subsequent court decisions, Law often only means what the Judge thinks about something.