Given that the key to Guerrilla warfare is that you hold onto no one piece of land how do you handle a spy (of any age)? You can not put him in prison, for that requires you to have a secure area (Which Guerrillas do have, but reserved for supplies and training NOT for holding prisoners, the main reason is if the secure area is attack, the defense is limited to delaying the attack till everyone else is out, prisoners are NOT that easy to move).
Thus guerrillas, sooner or later, face an unpleasant situation. How do you handle a spy given that you can NOT jail him? You have three choices, Kill them, release them or punitive punishment (i.e. whip them). Whipping them or releasing the spy permits whatever information the spy has to get back to the enemy. Thus execution is the norm with guerrillas. Surprising, whenever a Guerrilla army converts to conventional action, such executions drop, basically for the reason they now hold territory and can set up prisons (This happened in 1974 during the fall of Vietnam). Now we have to be careful the conventional attack MUST be based on a good chance of success, if the chances of success is slim and the guerrilla expect to revert back to guerrilla warfare at the end of the conventional action, such executions continue (This is what happened during the TET offensive of 1968 in Vietnam).
The problem with the Taliban is they are fighting a Guerrilla war. Apparently they hold onto most of Afghanistan but can NOT stop American (or its allies) moving at will throughout Afghanistan (This was the same situation in the 1960s in Vietnam). In the area not under Taliban Control, the Taliban can also move at will but have to be careful to avoid US or allied troops (i.e. the people tend to support the Taliban and thus will not turn them in and in face will guide them around dangers and even give them food and a safe place to sleep, again what the Vietnamese did for the Viet Cong in areas of South Vietnam under the control of the South Vietnamese Government). I will not go into what happened in Vietnam after 1968 (The US and South Vietnamese Government slowly, but surely took most areas of South Vietnam out of Viet Cong hands and into the hands of the South Vietnamese Government but never destroyed the ability of the Viet Cong to move at will if the Viet Cong just avoided contact with US or South Vietnamese forces, thus when North Vietnam send in conventional forces in 1972 and again in 1974 the Viet Cong could re-appear and asst the offensive, in 1974 permitting North Vietnam to take over all of South Vietnam, notice by then most of the Guerrilla activities had died down do to the lost of control of much of Rural South Vietnam by the Viet Cong after 1968).
I bring up Vietnam for the US is in a similar situation in Afghanistan today as it was in 1965, a rural revolt against the Central Government (The Taliban in Afghanistan, the Viet Cong in Vietnam), funded by outside sources (North Vietnam with the Viet Cong, Saudi Arabia/Pakistan intelligence services and other radical Islamic groups as to the Taliban). The US knew it had to defeat the backbone of the Viet Cong, its support from the peasants and that require infantry to occupy as much as the country as possible. Thus in a country less then 1/3 of the area of Afghanistan, the US committed over 10 times the number of troops. This high level of Infantry permitted the US to slowly suppress the Viet Cong. Now Vietnam had a much higher population then Afghanistan do to the fact it was and is a rice growing area as opposed to the wheat/herding semi- desert area of Afghanistan. Furthermore the Taliban are not the Viet Cong. Not withstanding these differences, the fact that the US has 1/10th of the Troops in an area three times as large does NOT get me to believe that the US has a winning policy in Afghanistan.
South Vietnam area:
173,809 km2 (67,108 sq mi)
http://en.wikipedia.org/wiki/South_VietnamAfghanistan Area:
647,500 km2, 251,772 sq mi
http://en.wikipedia.org/wiki/AfghanistanUS and Allied troops in Vietnam:
United States: 536,100 (1968)
South Korea: 312,853,
Australia: 49,968 (1962–1973)<[br />Thailand, Philippines: 10,450
New Zealand: 3,890 (1964-1973)
Another source gives these lower numbers for South Korea and other allies in Vietnam:
South Kora has 50,000 troops in South Vietnam
7,672 combat troops, New Zealand's 552.
10,450 Filipino troops
Compare those totals to what the US has in Afghanistan:
The US has only 48,000 troops in Afghanistan
http://en.wikipedia.org/wiki/War_in_Afghanistan_%282001%E2%80%93present%29In the Soviet war in Afghanistan the Former Soviet Union committed 118,000 troops, twice the number of US Troops in Afghanistan.
http://en.wikipedia.org/wiki/Soviet_war_in_AfghanistanNow today's US army is more technically advance then the Soviet Army of the 1980s and even the US Army of the 1960s, but when it comes to OCCUPYING a Country, it is infantry that does the job NOT technology. People tend to forget when it came to moving a huge number of men into a country the US showed it could do that in 1965 when the US first sent in troops to Vietnam. Similar attacks where done by the Soviets whenever they moved into Afghanistan (And the US show it could do it easily in Panama, Grenada and even in the liberation of Kuwait in 1990). The problem is none of these types of attacks are of any real value against guerrillas. Most Guerrillas when such attacks occur, come out of their hide-holds without their weapons and watch the show. That is all they can do. The problem is how to relate that massive movement to every village in the country? The Answer you can't unless the village people want it do so. Thus sooner or later the attacking forces have to break up and try to occupy the villages to force them to comply with the change caused by the rapid attack. The Villages raise objections via guerrilla activities which must be suppressed if the army that took the country whats to hold the country. Thus you have the traditional military rule of thumb, it takes three times the number of troops to hold onto a country then to take it.
Now, back to this execution. It is a sad face of Guerrilla warfare that such atrocities occur. We can dislike them but we have to understand it is part of the process of fighting a guerrilla war. It is not religious in nature, it is inherent in any guerrilla war, done by the Chinese fighting the Japanese during WWII, Poncho Villa against the Mexican Government during the Mexican Civil War, FARC in present day Columbia, and even the US in the fight against the British during the US War for Independence. These atrocities are ignored for most historians are uncomfortable with them. When they come up it is an attack on some group the Historian opposes (For example similar stories told of the Reign of Terror during the French Revolution, during the Paris Commune of 1871, various nasty strikes during the late 1800s early 1900s in the US. These are all periods of stress with people worried about security and spies and facing no sure way to prevent such spying except by execution. I am not trying to justify the execution but lets keep it in context. Yes, this is being done by the Taliban, but they oppose the US occupation of Afghanistan. As long as they can oppose the occupation but not drive out the US the Taliban has to use such tactics as unpleasant as there are. It is the fault of being at war not anything else.