Well, the other concern here is that this Marine felt that he could not contact his chain of command in regards to these nightmares and issues that his father reported he was facing. Two things come to mind; one, he was scared to admit to it and be pointed out, or felt that it would be ignored, or two, he brought it up and nothing was done and he still faced an additional deployment.
Truth be told, I have several buddies who have been on tour, and a couple who are returning for their 2nd or 3rd tours and each has their own experiences that they care not to share. Duty and Honor keep them going, but they have been and will continue to face some personal challenges with dealing with the things they have seen.
This Marine does not necessarily give all Marines a bad name. He made a mistake, and now has to face ridicule and questioning. Hopefully some good will come from this. Regardless if anyone argues he is a coward or not, it is unfair for any other American to judge him, unless they have faced the same circumstances themselves.