In some states, the CCW permit or CHL avoids the NICS check.
Gee, I hate to play Devil's Advocate but one could conceive of one NICS table at the show - so you avoid the dealer but pay a minimal fee.
And if you want to make the argument of convenience - oh, NICS is slow and you have to wait - I would counter that if such procedures did prevent illegal sales then you having a touch of inconvenience is just tough whatever.
The argument against such laws and/or procedures has to be made on their ineffectual nature, not inconvenience. You could also argue on the grounds of the 2nd Amend. says that .... - however, given that permits, FFLs, etc. already exist to regular possession - pragmatically, that will be seen as a rant and will have no purchase.