I think, perhaps, that the point has been missed.
If the Marine in question did, in fact, knowingly shoot and kill an unarmed Iraqi who was technically and legally classified as a non-combatant, then yes, he did break the ROE. And if that's the case, then he should be punished.
However, I think the major gripes that a lot of the people (myself included) are as follows:
1. The matter is one that is highly dependent on both the Marine's judgement, the situation, and any number of other things. To question the Marine in question's actions, without knowing the full facts and to not give that Marine (who has most likely been separated from his platoon--his family--since the incident, and been forced to deal with his concience alone) the benefit of the doubt, is appalling in itself. If the facts prove that the Marine was at fault and acting maliciously, then the Marine will be acquitted, and vice-versa. Until then, I think it is important to remember that this young man could have been any of us or any of our siblings, and I for one wouldn't hang my brother or sister out to dry.
2. The media. People talk about how the media shouldn't be allowed in combat zones, etc. Personally, I think it's a good thing to have them there, most of the time. They provide a civillian's perspective to ongoing operations, and in most cases, they tend to present a fair and heroic picture of what we're doing in Iraq and other places. That sort of thing works more wonders than all the recruiting posters or videos ever made. The real problem comes about when the media is so desperate for a story that they'll report anything, regardless of how irresponsible it is to do so. If you want an example, look at Giraldo Rivera (sp?) during the opening stages of the war. That is the kind of stuff that doesn't need to happen, but people push the issue and it does.
And when a reporter gets caught trying to send signals on camera that reveal the unit's location and future targets, that puts people's lives in danger.
Personally, I've got quite a few friends over in Iraq right now, with more on the way. I've already had a few give their lives, and I'd prefer not to have any more do so, especially not because a reporter either gave away secure information or prevented them from doing their jobs by second-guessing their decissions.