That brings us to the initial point that while gun ownership and rights may be justified and better for the citizens. Arsenals of automatic weapons and thousands of rounds are not.
Also, your bulletproof guidelines are just rules which apparently thousands of people fail to follow yearly.
I'm not saying that they're all legal but certainly enough to prove the point that while legal guns might be used to thwart crimes they are also used to commit crimes and quite a lot are stolen from actual legal owners.