You seem to think that it's OK for any/all level of government to make it illegal to be armed so long as some government-authorized subset of the population is government-authorized to possess government-authorized arms under government-authorized restrictions. I don't know where you get that.
From your prior reasoning (esp. the bit analogizing library cards), the states could ban guns outright, and the feds could ban guns so long as there is an exception for Irish-descended midgets wielding muskets while on patrol for the UN in Nigeria.
"and the feds could ban guns
Under the power of ... what?
"the states could ban guns outright"
Some guns (if it's not against the state constitution), yes. Not all guns. If they banned all guns they couldn't have a well regulated Militia.