So - nobody has a valid reason not to pass a federal UBC law, or at least I haven't seen one. We don't know how many guns have been bought at a gun show from a non-FFL seller where no BC was done, but I guess that's okay. We don't know how many shootings have occurred by someone with one of those guns, not just a mass shooting but any shooting. We don't know that, but I guess that's okay. And until such a federal UBC law is passed we don't know how many people will be shot in the future as a result, but I guess that's okay too.
Would any law-abiding citizen be denied his/her 2nd Amendment rights? NO. They gotta pass a BC anyway to buy a gun at a store that sells them or online, or even from an FFL vender at a gun show.
But who does get denied their 2nd Amendment rights? The people who can't pass a BC. Maybe they'll get a gun some other way, by stealing one or buying one on the street or through a 3rd party that can pass the BC. That UBC law wouldn't be perfect, right? All it does is close off one avenue to acquire a gun, and IMHO that is not a bad thing. And the thing is this, how is anyone else harmed? It's no skin off my ass, right? Or yours, so where's the beef?
With that, I'm done here. Have a nice day.