His defense lawyer, Haytham Faraj, is claiming that he had no choice, because "Marines in combat don't challenge orders."
I can only quote Thoreau:
A common and natural result of an undue respect for the law is, that you may see a file of soldiers, colonel, captain, corporal, privates, powder-monkeys, and all, marching in admirable order over hill and dale to the wars, against their wills, ay, against their common sense and consciences, which makes it very steep marching indeed, and produces a palpitation of the heart. They have no doubt that it is a damnable business in which they are concerned; they are all peaceably inclined. Now, what are they? Men at all? or small movable forts and magazines, at the service of some unscrupulous man in power? Visit the Navy Yard, and behold a marine, such a man as an American government can make, or such as it can make a man with its black arts--a mere shadow and reminiscence of humanity, a man laid out alive and standing, and already, as one may say, buried under arms with funeral accompaniment, though it may be,
"Not a drum was heard, not a funeral note,
As his corse to the rampart we hurried;
Not a soldier discharged his farewell shot
O'er the grave where out hero was buried."
The mass of men serve the state thus, not as men mainly, but as machines, with their bodies. They are the standing army, and the militia, jailers, constables, posse comitatus, etc. In most cases there is no free exercise whatever of the judgement or of the moral sense; but they put themselves on a level with wood and earth and stones; and wooden men can perhaps be manufactured that will serve the purpose as well. Such command no more respect than men of straw or a lump of dirt. They have the same sort of worth only as horses and dogs. Yet such as these even are commonly esteemed good citizens. Others -- as most legislators, politicians, lawyers, ministers, and office-holders -- serve the state chiefly with their heads; and, as the rarely make any moral distinctions, they are as likely to serve the devil, without intending it, as God. A very few -- as heroes, patriots, martyrs, reformers in the great sense, and men -- serve the state with their consciences also, and so necessarily resist it for the most part; and they are commonly treated as enemies by it.
What a shame for Corporal Thomas and his victim - or more likely, victims - that he had the bad judgment to submit his conscience to that of the government of the United States; what a shame he was naive enough to let his admirable desire to serve and his respectable courage be twisted by the "black arts" of the military-industrial culture, until he was made something less than a man, a mere killing machine of flesh and bone.
Of course that culture wants it both ways; it trains the men (and women) it assimilates into unquestioning obedience, then when one does wrong asserts that "I was only following orders" isn't a legally valid defense.
What's even odder is that these kids are sucked in by patriotic rhetoric, when in fact the Founders were opposed to standing armies. The modern military is exactly the sort of institution that the Framers of the Constitution wanted to avoid. They preferred that "well-regulated militia" mentioned in Amendment II. (That's also why Article I, Section 8 says Congress shall have the power to "raise and support armies, but no appropriation of money to that use shall be for a longer term than two years.")