There's quite a bit of difference between changing the Constitution on the one hand, and changing the law on the other, particularly because many people (including many Constitutional scholars) believe that many portions of the GCA are unconstitutional (whereas some people merely disagreed with the 13th Amendment...but that issue had been settled in 1865). Additionally, the mere sale or transfer of firearms, in and of itself, harms no one - something that cannot be said of slavery.
As for the acquisition of an FFL - the item, in and of itself, is violative of the Constitution. Further, and more to the point, how do you ***know*** that all of those "kitchen table" dealers had no intention of selling guns? Many of them actually did, although they didn't have their stores behind a plate glass window on Main Street with regular hours. Who are you, or the Feds for that matter, to tell people precisely how to conduct their business? Maybe someone wanted to buy lots of guns, use them for a while, and then be able to sell them to people in various parts of the country? Doing so without a license was and is illegal (though, again, I believe the whole concept of the FFL is itself unconstitutional), so these people paid their fees and submitted to background checks. What's the problem?
You can't use a pre- to justify some action post-. Neither with slavery or with guns. What's past is past. Saying, "We used to be able to ..." is not an argument I'm willing to consider.
"how do you ***know*** that all of those "kitchen table" dealers had no intention of selling guns?"
Well, let's just say that going from 284,000 "dealers" to 54,000 dealers in a very short period of time was my first clue.
"Who are you, or the Feds for that matter, to tell people precisely how to conduct their business?"
The feds bees the ones with da licenses. THAT'S who they are.
"As for the acquisition of an FFL - the item, in and of itself, is violative of the Constitution."
Violating what part? (Please don't say the 2nd amendment. I'll be so disappointed.)