Why shouldnt all private gun sales be subject to background?
Because it is illegal. Bet you didnt know that, did you? Private sellers are expressly barred from the NICS system that gun dealers use to run those background checks. If they were not, most would be very happy to run the check. Personally, when selling a gun I will only sell to someone with a concealed carry permit, so I can be sure that no one who should not be able to buy a gun buys one from me.* So get that prohibition removed (as gun rights legislators have tried to do, several times) and presto, problem solved. *I mean, thats what I WOULD do when selling a gun, if I had any to sell. Unfortunately, all of mine were lost in a tragic boating accident.