The constitution is not a suicide pact. There was a time in America before cops were saddled with a political agenda and were actually concerned about law and order, that this kid would have been separated from his guns at the very least and monitored.
And cops aren't psychiatrists - they are law enforcement officers. They have limited powers for a purpose. The dude should have been handled differently by those who knew him well - calling the cops for a case like this is a cop-out, not a solution.