They weren't in "public". They were on their own property, defending themselves against a riotous mob that threatened to kill them, their dog and to occupy their home. Some individuals were even pointing to different Windows and telling the McCloskey's which rooms that they would take.
No "fine line" was crossed by the McCloskey's, but a broad line(fence and gate) was crossed by the "peaceful protestors" when they TRESPASSED on to private friggin property.
BTW...how does one defend one's self with a gun without "brandishing" it. For it to have any effect in staving off a mob, it has to be seen by said mob.