the public safety component
A concern for public safety with respect to guns, knives and clubs was hardly existent at the time the Constitution was conceived. People lived "by the gun" back in the day. Weapons were no big whoop then. If anybody would have mentioned the words "gun permit", most likely they would have been laughed out of town. Heller made it abundantly clear that what a law meant when written is still what it means today. Also bearing is how a law was applied by the courts in the immediately ensuing years after passage. Insofar as the Second Amendment goes, there appears no notable gun regulations related to public safety. Public safety via weaponry is a modern day issue not addressed by The Constitution, and is thereby irrelevant in the current proceedings.