1) Background checks are not universally mandatory in the states and the databases used for them are not coherent.
2) There is nothing preventing someone selling to a criminal or mentally ill person in a private sale since background checks are not required.
3) The NRA lobby does an excellent job making sure there is no oversight or no funding for that oversight. The ATF is well aware of a small number of gun dealers who provide the majority of 'illegal' guns used in crimes but federal regulations and lack of staff prevent them from following up.
4) Your use of the term "arbitrary" is in fact the opposite of what is proposed, a figment of the paranoia spawned by the US gun lobby.
As you and wilber have stated, Canada already requires background checks for all owners yet Canada still has one of the highest rates of gun ownership per capita. You might feel inconvenienced because you have to lock up your guns and thing the government knowing about you is an invasion of privacy but our laws seem to strike a pretty good balance. Meanwhile in the US the gun lobby heavily fights against anything even related to ensuring safer gun ownership.
1) Background checks are required in every single state at the retail level, buying a gun from a gun store isn't like picking up a jug of milk or pack of toilet paper.
2) That's like saying there's nothing stopping an underage kid from buying booze from a friend who is old enough...nothing except the
law.
3) The regressive left does a great job pandering to its base and perpetuating misinformation about firearms, their operation and their owners. "Assault weapons" which are already a misnomer, accounted for like 250 deaths in 2014 or a single digit percentage but they're being deemed "too dangerous to own" because of cosmetic and ergonomic accessories and features.
4) Yeah, arbitrary. How else do you explain a century old technology, semi-automatic fire, is suddenly vilified because of how it looks.
Yes, there is an automated background check component and thankfully, with registration gone, I no longer have to report at point-of-sale, which is really what gun grabbers mean by "universal background checks". The idea of verifying the criminal history of a prospective buyer of your secondhand firearms would be a lot more palatable, if it didn't imply point-of-sale recording, that would be an actual compromise; but gun grabbers don't want compromise, they want concessions.