What's effective, and affecting, about this video is not just that the young veteran politely criticizes Obama on the point that made his candidacy within the Democratic party. (Obviously one can argue with the substance of what the young man has to say -- notably his ridiculous claim that "Iraqis are just like us.")
Rather, the real effectiveness of his video comes less from the words than in the sincerity and personal nature of this veteran's commitment to those words that gets demonstrated visually when he walks away from the camera. It is ironic that this mode of visual persuasion was originally (and, even more effectively) used by the epic anti-war documentary "Hearts and Minds," which won the Academy Award for best documentary in 1975 (and which the same kinds of people who probably like the video above excoriated as a hachet job). What makes both the video above and "Hearts and Minds" so moving is the way that passionate, sincere words are given forceful weight by a visual trick which, after the intellectual argument is made,seals the case by visually "proving" the commitment of the speaker. (Only a cynic would argue, in both cases, that the personal sacrifices of the speakers delegitimate what they have to say: in the case of the video above, is the veteran merely desperate to ensure that his personal sacrifice was not fruitless? in the case of the anti-war veterans of "Hearts and Minds," are they merely displaying bitterness over their personal sacrifices?)
Clay Shirky has more.
Update: The original version of this post incorrectly implied that this video was produced by the McCain campaign. In fact it was produced independently, in support of the McCain campaign, much as Will.i.am's video was produced independently, in support of Obama. I have changed the wording of the post to make this distinction clear.