The OP is a false statement on its face. I cannot go into a gun store and walk out with a gun today. It is not like buying a t shirt at Walmart.
No it is not as easy as buying a T shirt, and it should not be. However it is easy to buy a gun without any background check from another person, or in the parking lot of a gun show, or by a straw buyer.
So your post reflects your ignorance, and/or that you are a damn liar.
I'm sure you are aware that, at the very least, no person is allowed to sell their firearm to another if the other isn't allowed to possess the firearm, aren't you?
Private Gun Sale Laws by State - FindLaw
And I'm sure that happens everyday, and you know that too.
If every gun were registered, that issue could be resolved. Not in the sense it will prevent all gun sales to those who are not vetted, but to link the sale to the registered owner, and punish them. Of course that too won't prevent gun violence, but it sure would limit the number of those intent on criminal activity to obtain a gun.
But I believe each state should be allowed the right to require licensing of all gun owners, and the registration of all guns within their borders.