The Marines should be punished but nothing that wrecks careers. But it isn't just about those particular Marines.
One, if this is a sign of lack of unit discipline, the incident must be addressed and looked at from the point of view of how those troops are being led (or not led, as the case may be). We really don't want to give the enemy propaganda material. This really is a readily digested outrage amidst the carnage of war. What the Marines did wasn't that bad, in isolation, but we can't allow things like this to go on lest it help enemy recruiting. If the problem is leadership shortcomings, consider ourselves lucky this was just a corpse wetting and not something worse. Deal with it now.
To be clear, this incident won't cause Afghans to become jihadis and commit terrorism. They did that just fine all on their own before ever seeing an American Marine or soldier. But it does provide a convenient excuse to kill Americans in a barbaric manner. Even better from the enemy point of view, it lets gullible Americans argue that the incident "causes" jihadi anger. We should at least make our jihadi enemies work hard to come up with their flimsy excuse-of-the-moment for why they are vicious terrorists who want to murder us in our homes.
Two, it highlights the potential problem of all that battlefield surveillance video out there. War is awful and if you film it, you'll naturally be horrified at what is done even when all the rules are followed. The Greatest Generation's reputation wouldn't have survived the same level of visual recording. We can't allow our surveillance video to be combed for out-of-context images of apparent outrages or crimes.
But the enemy reaction does seem to offer a surprising avenue for us to exploit:
"Our leaders overlooked this degrading and inhumane act of American soldiers because they are interested in peace talks," said Mullah Mohammad Gul, a local Taliban commander in southern Helmand province, where the video is believed to have been made.
"Our duty is to defend our sacred religion and our people and we will keep fighting, no matter what."
Insurgent fighters in other parts of the country said the video could undermine discipline and push foot soldiers to ignore orders from higher ranked fighters.
The Taliban leaders understand that they are getting their butts kicked. At ground level, that reality isn't as obvious for many of the Taliban in the field. So the leaders have a choice of negotiating to get better conditions for success (and calling off the drones that make Taliban rear areas as dangerous for leaders as the front is for the cannon fodder)--but risk losing control of their men; or, in order to keep their men with them, let the war continue at our discretion, which means we continue to make progress on the ground despite the willingness of many Taliban to fight us and continue to target the leaders with all of our forces.
So often, our enemies seem to like to talk just to weaken our will to fight. This could be an opportunity for talks with no objective other than having the enemy frontline gunmen see their leaders chatting it up with smiling NATO negotiators.