The argument I have heard is that a universal background checks system would require the government to keep a registry of gun owners to be at all useful. You have to be able to go back and prove whether a seller performed the proper background check before selling a gun to a particular person.
A possible alternative I thought and have always wondered why it doesn't get used would be some sort of private public key cryptography where the seller would get a signed certificate proving they ran a background check and it's result, but the government wouldn't store anything.
A possible alternative I thought and have always wondered why it doesn't get used would be some sort of private public key cryptography where the seller would get a signed certificate proving they ran a background check and it's result, but the government wouldn't store anything.