As a potential future lawyer who has been paying attention to the law, what are the primary objections to ISLT? Personally, I think the strong variant is batshit crazy, but the weak variant is more logically sound to me. I think the textual support is quite strong. I've heard that the counterargument would be based on historical precedent, saying that goes against how things were done in the past, and I think you allude to it here, "More than 170 state constitutional provisions, 650 state laws, thousands of rules and regulations, and hundreds of state court decisions would be thrown into question."

Since the States and the federal government are both sovereign, that means both are operative. And the federal government gives the power to the State legislatures. But the State legislatures are still bound by their own constitutions. Therefore it seems to me, that regardless of what the ISLT says, the States are still bound by whatever restrictions are in their own constitution, as well as State court precedent interpreting said constitution. So there might be a conflict of law issue, in which case, judges attempt to reconcile both, which might be difficult. But I don't think the Supremacy Clause can be interpreted to override the State constitutional provisions at issue, since the whole point of the system is that the people from each State send representatives from their States and the States themselves send representatives to Congress.