sadly, they had no choice
But I feel real badly for the wife and family. He could just as easily have run up the aisle screaming "I'm the President of the United States, put me on Air Force One" and he'd be alive, but hospitalized, today. He was having a psychotic episode. He did not "deserve" to die, but the marshals had no way of knowing and they did what they were supposed to do. I expect they are sad to find to learn the guy was mentally ill and off his meds too.
Compassion is good, and it costs nothing.