On the surface, that seems like a generally good idea. I'm not sure how it would work in practice, though. If there a hearing and a trial, the "allegator" (to use your word) will probably be the U.S. Marine Corps. And if there's a not guilty verdict it's hard to see how the USMC should pay damages if they acted in good faith.
I suspect you'd rather go after Murtha and other commentators who are talking about this case. As repugnant as we find these people, I don't see how anyone could legally go after them just for making comments.
These people know the rules of evidence as well as anyone. They all probably know the ins and outs of logical fallacies better than most.
My accusation is that they disregard rigorous analysis and insinuate reprehensible behavior to others in order to advance their own agendas or to enrich themselves.
Once their allegations are proved to be false, would you endorse pursuing them with libel charges?