Ok now you've truly baffled me. You'll accept that barring guns from certain places means there will be nobody armed to stop the bad guy, or you'll accept the opposite?
Can't do both without violating causality and sending the entire Universe down a wormhole, so answer carefully.
What I am saying is this - we as a people have a right to decide that there are places like schools where no person other than armed security should bring guns there. Airports and government buildings like courts would be another such example. In addition, there are private buildings that can decide for themselves that issue.
If a person attempts to kill people in that setting and a customer or visitor stops them with their own gun that they were not suppose to have I would welcome their intervention if it saved lives, hurt no other people and look at it as a practical and realistic event which happened despite the written law.
Did they violate the law? Yup. Did they do what they were not suppose to do? Yup. But given the circumstances of an emergency situation and the positive result that ensued in saving lives - that can be overlooked.
I would consider such an event to be the rare exception to the rule and something which is fairly rare and not something which should guide us in setting policy because of that.
However, as a matter of law and as a matter of what kind of society we live in - I support such designations where appropriate. I am on record as agreeing with the NRA that there should be armed security on duty at every school in America. I support such a proposal and think it is a way to avoid turning American and every place in it into some 21st century version of the mythic Old West where everybody walks around armed until they end up on Boot Hill. I believe that - in the end - such society will only have more deaths and more killings and more suffering and the policy would do more harm than good.
Is that a contradiction? perhaps it is in a way if you are looking for a "gotcha" moment. I think not however. What I advocate as public policy and what I can tolerate and look the other way at in a very rare exception turned out positively - I believe - are two different things that are simply practical and pragmatic.
I can think of other examples - I support speed limits and enforcement of them but if a person is rushing someone in great distress to a hospital and they exceed that speed limit - I can look the other way providing they injure nobody in the process.
I believe in realistic pragmatism and looking at exceptions as rarities and not something to set public policy by or for.
I hope that answers your question.