BURN THE GENEVEA CONENTION! IT WAS NEVER MEANT FOR AMERICANS, IT WAS WRITTEN TO PROTECT OUR ENEMIES ONLY!
Well, its intent was to try to protect civilians and third party noncombatants more than to protect combatants on either side of a conflict. The idea was to make it more attractive for warring parties to to follow some rules of engagement and restraint, rather than to use noncombatants and their property as 'shielding' or 'cover' by disguising soldiers as civilians or hiding military assets among schoolchildren, residents, hospital patients, and captives in prisons. When combatants among defenseless people or shoot from among them, the other side has little choice but to attack, even at the cost of innocent lives. The convention was designed to offer warring parties a reason to restrain themselves from using defenseless people as human shields.
The problem is that if your side has no respect for human life, then the Geneva Convention has little to promise you. If anything it would make fighting more complicated for you. This is the case with terrorists since folks like al-Qeada, being foreign to Afghanistan and not even particularly concerned with anyone other than themselves, could care less about Afghan civilians and for the most part saw the civilian population of Afghanistan as a means to shield themselves from US strikes. Likewise, hard-line Afghan Taliban leaders had little problem with using civilians as cover for their stashes of weapons. Not all Taliban members are like this- some more moderate Taliban members and Afghan commanders don't want to cause harm to civilians, particularly their own families or tribes, but sadly for Afghanistan way too many don't care at all about 'Afghanistan' and only want power for their respective faction. That means the lives of those not considered 'beneficial' are cheap.
This 'life is cheap,' mentality means that terrorists have more options in fighting a war than a nation or group of soldiers who are reluctant to kill civilians, captured prisoners, or noncombatant third parties. Lawful combatants are at a disadvantage because they have to be concerned not only about their own soldiers, but also about the casualties that might occur to third parties, enemy or friendly civilians, prisoners in their care, and neutral noncombatants. By encouraging combatants to fight according to rules of engagement and 'rules of war' the civilized nations made fighting other lawful combatants more difficult, but at the same time made it easier morally and legally to be relentless against lawless forces who use civilians as camouflage.
Terrorists don't need to take care of their civilians or prisoners, and therefore have less to deal with in terms of materials and manpower- they don't have to feed or care for civilians or prisoners, and do not have to set aside fighters to guard captured enemy personnel, and do not have to provide care and safety for prisoners. If you are unpopular in a country, as most thugs are, but want to fight a vastly more powerful, though ethical foe, you don't want to follow the Geneva Convention because, quite frankly, you will lose the few advantage of being a terrorist - the safety afforded by operating among civilians and the freedom of action of those who do not need to concern themselves with protecting noncombatants. Terrorists exist only because civilized nations are reluctant to kill even terrorists, much less innocents in the way. Terrorists want and even need to use the conscience and legal nature of their enemies to advantage.
Technically speaking, the Geneva Convention was designed to make fighting easier for us and for like-minded western nations who are traditionally reluctant to hit unarmed people just to pick off a few scumbags. The convention EXCLUDES people who adopt terrorist tactics so that there would be a legal framework- essential for nations and groups which adhere to the 'rule of law'- to make it possible to justify fighting terrorists even when civilians are being used as shields by the enemy and might be endangered.
If both sides are adherents to a 'rule of law' and consider themselves obligated to protect their civilians and their captured soldier's lives, the convention offers distinct advantages and therefore such nations will tend to abide by the convention in order to ensure that its people will be treated in the same way. So the convention works with civilized nations to varying degrees, depending on how ethical they are, how much they want to protect their own people, and how great is their desire to minimize casualties on both sides while still obtaining their objectives in war. Restraint in warfare under the convention will then hopefully result in benefits like lower casualties and better treatment of prisoners or the citizens of occupied territory, even though it limits a nation's military options against an opponent with its own lawful combatants and rules of engagement.
The sort of conflict the Geneva Convention regulates is less common these days, since lawful nations are less and less at odds with one another militarily since nuclear weapons put disputes in stark perspective. It is now less likely we will face another 'rule of law' western nation in open warfare; I doubt we would ever find ourselves in battle against Britain, Australia, Canada, Switzerland, Mexico, or most of Europe. We may well face non-western nations like Iraq or Iran which do have a 'rule of law' of sorts, however. But they, being at an extreme disadvantage in 'lawful warfare' verses the US's much greater power, may opt to use not only organized and uniformed 'armies,' but also may use terrorist assets. Thus their uniformed and identifiable personel will be treated as POWs while terrorists and other unlawful combatants will not be considered as such. The convention is utterly useless to discourage terrorists precisely because they are by definition 'lawless,' and that is why the convention offers terrorists no protections. It simply isn't meant for them.
That said, it doesn't sound like our SEAL surrendered, since they were dragging him. Perhaps they were struggling with him and decided the struggle wasn't worth it and shot him. If so, that is part of war. If he didn't surrender and didn't give up any of his equipment or weapons still on his person, then that is war. It's ugly, but we do the same thing to people who don't disarm and surrender... we're not obligated to risk lives on the battlefeild by trying to disarm people who haven't surrendered- we're not policemen.
To be blunt, if I were over there I wouldn't surrender to those scumbags either, knowing how they do treat prisoners and even their own people. It's better to get shot than it is to get taken off and skinned alive.
But it is probable they weren't struggling with him and he had been rendered unconscious or so disabled he could not resist, and they were dragging him for that reason. If that is the case, and they shot him, or tortured and then executed him while bound, then they have violated the rules of war. Only the video would make this clear.
In any case, it was evidently some 14 hours before his body was hauled out. It may be he was shot within a short time after they got their hands on him and we retrieved the body 14 hrs later, or it may be our forces sent to get him out engaged in a battle, and the scumbags killed him during the fight. The term being used in the press is execution, which implies that he wasn't killed in the line of fire nor killed during a fight when keeping prisoners would unwise. Either way, I hope that the fact that his body was retrieved is an indication that the folks who killed him are now dead and cannot live to tell of it.