Personally, I don't believe in moral absolutism - I think our morality should be reasoned & justified based on the situation - besides "harm caused" is a better judge.
The actions of the soldiers are liable to cause emotional harm to the family of the people on the film & this act was meant to dehumanise them, the act brands the dead as "less than human" - in society we already know full well the dangers of these kinds of actions & should rightly combat it.
We should condemn all involved in this incident, along with any violent repercussions of this & what happens when US soldiers are caught.
In this case it's more of a moral consistency that's the point - it's rational to act in such a way in which you want to be treated.
If person A does not wish to be killed - it's irrational for person A to kill people randomly - because he would be appealing to a set of values he does himself possess, there would also be no reason for others to respect his wishes.
The same applies to this situation, if we as as society don't want the remains of our soldiers to be desecrated, it's morally consistent to not do the same to them.
The age old line "Treat others how you wish to be treated" is the basis of most of our social evolution & one of the most important things people need to understand.
I do believe morality exists - but that's based upon a specific definition, for me a moral act is "reducing total human suffering" & an immoral act is "increasing total human suffering".
As suffering is something we can measure (neurobiology/brain scans/psychology) it's somebody which can be objectively defined.
http://www.samharris.org/site/full_text/the-moral-landscape/
A very good read to anybody who has an interest in morality.