It all started on 911 as the movie shows you..
NOTHING happened BEFORE that ..so don't go poking around looking ok ?
If you know what's good for you ?
You will watch the movie then feel sorry for the poor Americans.
Then don't ask any questions.. kapiche ?

Please list the "lots of developed democracies" (preferably with citations) where sleep deprivation, subjecting a prisoner to noise, and stress positions have been found to be legal, to the degree that those practices were performed at Guantanamo.

You supported your opinion nicely.
Entropy ain't what it used to be.

Oh proper bullish!t reply that doesn't understand the difference between fact and opinion.
Fact: Long term sleep deprivation can cause damage to the mind and body, and causes suffering.
Fact: Torture is the act of inflicting pain on someone.
Ergo, sleep deprivation is torture.
http://www.pbs.org/newshour/rundown/torture-can-affect-brain-leaving-long-term-psychological-scars/
http://www.theatlantic.com/health/archive/2013/12/how-sleep-deprivation-decays-the-mind-and-body/282395/
Piece the facts together for yourself.
~ I'm a 21st century man and I don't wanna be here.

Sleep deprivation IS torture. This is a fact.
Your "fact" is an opinion. Your source shares that opinion for cases of extended sleep deprivation, but it's still opinion.
Entropy ain't what it used to be.

Sleep deprivation IS torture. This is a fact.
https://www.psychologytoday.com/blog/dreaming-in-the-digital-age/201412/why-sleep-deprivation-is-torture
So is sexual assault, attacking people with dogs, forcing prisoners to take psychotropic drugs, hanging them from beams for days, pouring ice water on their genitals, sensory deprivation and making them think they're going to die.
Torture is torture.
~ I'm a 21st century man and I don't wanna be here.

There is no torture at Guantanamo, never has been. Unless you are going to define interrogation methods legal in lots of developed democracies, such as keeping people awake, subject tot noise, or temporarily in in uncomfortable positions as "torture."
As the European Court of Human Rights ruled, none of these are torture and that when used in Europe "did not occasion suffering of the particular intensity and cruelty implied by the word torture"
http://hudoc.echr.coe.int/eng#{"dmdocnumber":["695383"],"itemid":["001-57506"]}
Australia also rejects defining sleep deprivation as "torture"
http://www.abc.net.au/pm/content/2006/s1754821.htm

by the time captives got to Guantanamo Bay the CIA had already wrung them dry in black sites or by rendition to countries less squeamish about torture.
Abu Ghraib and Gitmo are/were military prisons, not CIA sites. Sleep deprivation and stress positions may have been more common torture in those places.
In his cloak of words strode the ringmaster