The Second Amendment to the U.S. Constitution states: “A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.”
Like most rights, the Second Amendment right is not unlimited.
It is not a right to keep and carry any weapon whatsoever in any manner whatsoever and for whatever purpose. The scope of Supreme Court rulings regarding this issue have, over the years, been unclear and have been claimed as victories by both pro- and anti-gun advocates.
As someone who has over 30 years military service and has handled everything from handguns to napalm to nukes, I can say that an “AR-15-style” rifle is not a defensive weapon.
Any person, such as the man carrying such a weapon near Big Al’s bowling alley, obviously has not read all the cases which, if nothing else, say that laws may restrict the carrying of weapons in public places.
Best thing would be for this person to join a well-regulated militia (i.e. the National Guard) where he can display his weapon properly and use it for what it was intended — provided he is intelligent enough to pass the entrance exam.