Actually... it makes perfect sense....and thats as far as the ATF should go.... interstate...not intrastate.
If someone does something inside of a state with a firearm the ATF should have nothing to do with it.
It actually makes sense to a degree. Different states have vastly different laws that it would be nearly impossible to be sure you are completely a legal sale. And you're right, interstate commerce does fall under the authority of the Feds.
I feel these two statements need repeating. I don't have the answer to #2, but it's far and away more important (IMHO) than #1.
#2 may be true, but practice has shown it to be uncommon. People also self-police fairly well in my experience. Like I said, it's damn near impossible to buy in Minnesota without showing an ID and doing a bill of sale where you attest to not being prohibited or being asked to show a permit to purchase or permit to carry.
"Closing the loophole" might not be so contentious with gun owners if the antis would accept that there ARE other methods of doing it outside of their registration scheme, but they won't allow that because they want the task to be onerous (gotta go through an FFL during business hours for a fee, in person, complete a registration...I mean 4473 form, yada yada).
I have heard the proposal made that there be a 1-800 number that private citizens can call. Use the social of the buyer and simply get a yes or no if they are able to buy. There is no record of a sale actually taking place or what firearm was being talked about, but it would give a seller the confidence to proceed and might discourage people from trying to make illegal purchases.
The antis of course immediately come back with the argument that there is no record of it ever being done and it's unenforceable to which I ask them how they are ever going to enforce the 4473 scheme on firearms made prior to whatever date said legislation is enacted without creating an illegal firearms registry. The usual response is crickets.