And how many of those were denied in error? You claim that 7000 denials in Colorado means 7000 criminals didn't get guns, and therefore didn't commit any crimes; that is a completely unsubstantiated assertion, because you have no idea how many, or even whether, those 7000 people were actually criminals at all. And you have no way of knowing they did not simply procure them by other means. Or someone just gave up on the idea of purchasing a gun altogether because these laws have made it an onerous and discouraging process..... a process that you would never tolerate on any other fundamental right, would you?
The statistics only show that 84,000 denials were not contested by the person who was not allowed to buy a gun from an FFL. That was in one year.
Did those people who couldn't pass a background check then resort to buying a gun from an ad on the internet? Don't know...but that is why I favor universal background checks..to make it as inconvenient as possible for those who can't pass a BC.
There is no "basic right" to sell a gun to anyone you choose. You keep confusing the 2nd amendment with the right to sell. The person attempting to buy a gun may have been denied the second amendment right to own a gun, but it has already been taken to court and ruled that the government does have the authority to prevent that purchase.
Are you arguing that it is unconstitutional to prevent an ex-felon from buying a gun? If so this is the wrong place for you to attempt to make that argument. Call your lawyer and take it to court. You'll never persuade me that you know more about the law than the courts do.