What this thread is not: a place to discuss the quest and the involved actors as it stands in-game; there are plenty of other places where you can do that, if you are so inclined.
Please answer the following examples for me. You may answer either as yourself (i.e., you the person entering the message) or as your in-game character(s), by which I mean you can examine these situations through your worldview or your character's (characters').
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Situation A: You are informed of Paarthurnax's alleged atrocities by Esbern or Delphine; however, they do not hold you to killing the dragon. Assume that neither Blade has any intention to deceive you and that their sources for this information are correct. Regardless of not being asked, do you kill Paarthurnax?
Situation B: The quest is identical to how it is in the game. However, you are informed of Paarthurnax's alleged crimes with exacting detail. As above, assume that neither Blade has any intention to deceive you and that their sources are correct. Do you kill Paarthurnax?
Situation C: The quest is identical to how it is in the game. However, there are absolutely no negative repercussions to killing Paarthurnax. Do you kill him?
Situation D: The quest is identical to how it is in the game, with one exception: Paarthurnax is not a dragon, but a wizened old man, similar to the Graybeards. Do you kill him?
Situation E: This situation is identical to the above, with one change: instead of being an old man, Paarthurnax is in his prime. Do you kill him?
Situation F: The quest is identical to how it is in the game. However, upon speaking to Paarthurnax, he explains that the accusations against him are true, and what's more, expresses delight in his past transgressions, but makes no move to harm you and never gives you the impression that he will. To clarify, his present demeanor is the same as it is in-game, but he discusses his past crimes with something like nostalgia. Do you kill Paarthurnax?
Situation G: The quest is identical to how it is in the game. However, when asking Paarthurnax about the Blades' ultimatum, he explains that their accusations are true. He does not express delight in his past, but neither does he express remorse. Do you kill him?
Situation H: The quest is identical to how it is in the game. However, when asking Paarthurnax about the Blades' ultimatum, he explains that their accusations are true. He expresses remorse about his past deeds. Do you kill him?
Situation I: The quest is identical to how it is in the game. However, when asking Paarthurnax about the Blades' ultimatum, he indicates that he will not blame you if you kill him (e.g., he claims that he is "ready to die" should you choose to act on the Blades' vendetta), despite the fact that he expresses neither remorse for nor pleasure in his alleged past deeds; he also does not indicate whether the Blades' accusations are true. Assume that, as in the game, you do not know whether the Blades' accusations are true or false. Do you kill Paarthurnax?
Situation J: This situation is identical to the above, except that the dragon admits that the Blades' accusations are true. Do you kill Paarthurnax?
Situation K: The quest is identical to how it is in the game. However, there is a dialogue option that will cause the dragon to fight you without you precipitating the struggle. Do you kill Paarthurnax?
Situation L: The quest is identical to how it is in the game. However, Paarthurnax has some rare, one-of-a-kind treasure on his body, such as a powerful weapon or piece of armor. Do you kill Paarthurnax?
Situation M: The quest is identical to how it is in the game. However, the act of killing the dragon, while required for the quest, is considered to be an in-game crime. Remember that there are no guards there to report or fine you, but it is still a crime. Do you kill Paarthurnax?
Situation N: The quest is identical to how it is in the game. However, refusing to help the Blades will result in you being unable to remove any followers you have inducted into their order from the Temple. Do you kill Paarthurnax?
Situation O: The quest is identical to how it is in the game. However, Delphine and Esbern may be killed instead. They are a relatively easy fight and do not offer any prizes of note. It is considered an in-game murder to kill them. Do you kill the Blades?
Situation P: The situation is identical to the above, with one exception: it is not considered an in-game murder to kill the Blades. Do you do it?