I haven't seen the video, but I'm going to assume it is someone IN A MARINE UNIFORM throwing a puppy over a cliff. First off, you need to understand that what you see is not necessarily reality, so whatever moral extrapolations you want to make need to include the very real possibility that this video stands in congruence with a long line of similar propagandistic acts.
Substantially the entire history of Vietnam as most people in the street understand it appears to have been fabricated. This would include alleged war crimes (most of them), drug use, and incidents of crime related to Post Traumatic Stress Disorder. Read Stolen Valor.
Secondly, if accurate, that is at a minimum "Conduct unbecoming a Marine". There is no combat value to that, and it is counterproductive. It would, I think, anger and sicken substantially ALL of our soldiers, who by all accounts do an outstanding job of maintaining their mental and moral health under very demanding circumstances.
This w/fs link is, I think, much more reflective of the general reality: http://www.msnbc.msn.com/id/18871405/
It is clear to me--and I am in the process of documenting the ideological transformatin by which this happens--that influential segments of our populace reject not just the American political system, but the values which define it. As some of the most noble exemplars of those values, soldiers come in for special attack, because they give the lie to the necessity of accomodation with evil.