[Rick Lee]

It doesn't mean you've been bad if you get denied. You could have the same name as someone else on the no-buy list. Lots of folks are on there who don't deserve to be, just like the no-fly list. You can be on that list with just an accusation of domestic violence.

The background checks are run by the FBI, but are totally a garbage-in/garbage-out thing. If a nutbag has a long histry of mental health issues, chances are very high that his state never reported it to NICS. So he'll have no problem passing a NICS check. Obviously, no one ever answers "yes" to the questions that would make you a prohibited possessor (are you a fugitive, illegal user of drugs, wife beater, illegal alien, convicted felon, etc.). So NICS weeds out the people with unfortunate names or who are too dumb or lazy to lie, get a straw buyer, take their chances or buy on the black market. Rest assured, no would-be bad guy has ever been denied in NICS and then decided he just wasn't going to be able to get a gun and so had better give up committing crimes.

No one has even proposed making NICS checks more thorough, so making more people go through them is going to stop the next mass shooter just as much as NICS stopped Loughner, Cho, Holmes, etc.