Using this logic, we'd have to rely on the law enforcement schedule to take care of any of our problems. You would not be assured of security in any venue, outside of law enforcement (think of private security at schools, retail establishments, concerts, cultural events, etc.). All we could do is call 911 and hope the problem does not encroach upon us too badly while awaiting law enforcement. Bad guys love that we are often in this mindset.
The victims may have played this one smarter. I wasn't there and do not know what threat they perceived at the time. But, the property owner was well within his rights to advise the perp that he was trespassing and must leave. That being said, I have always braced myself for bad reactions when I have done the same. I don't think I would have done what they did with only one firearm amongst the group.