I think it all boils down to this: As long as gun owners and gun purchasers believe they are getting something in return for the bother of going through NICS they'll go along with it and ignore any possibility that it
might be unconstitutional. So far, you've from several gunstore owners and they all seem to think it's a great idea. But it keeps them from getting sued every time a guy buys a gun from them and then goes out and kills his wife too, so they have a somewhat 'vested' interest in NICS.
A guy who yelled at his first wife (thirty years ago) when he found out she was sleeping with the milkman might take another view of it, especially if he now has a problem with varmints around his home.
Whether or not it is constitutional is a question that will have to be resolved in some future court case, not on this forum. It came into being as a
reasonable restriction on the right to keep and bear arms. It has since been amended to cover several other "reasonable" situations. Even now there is a push (aided by the NRA) to enact another "reasonable" amendment to it.
All this reminds me of those other great lies, like; "The dog ate my homework" and "The check is in the mail" or "I'm only going to put the tip in." Now we can add in "This is just a reasonable restriction."
My personal opinion (everyone has one, you know
) is that NICS is just another of the 'thousand cuts' we are going to die from.