Why Does Auron Act as Though His Arm is in a Sling?

[Hazzard]

The whole of the people in Spira were aware of Sin returning, how could you forget that?

The Yevonites thought that Sin would disappear for good when they had atoned enough for their sins. So I believe everyone hoped that Sin would be gone for good after every Calm. Only Yunalesca and the Maesters knew that Sin would always return.

I was wrong about the Final Aeon, though. No one knew it had to be a guardian, except Auron. But I do not believe that Auron knew about the corrupt head of the Yevon church, neither did he know about Sin always returning nor that Bevelle was filled with machina (I remember him making a sarcastic comment about it in the game).

Yes, but that's "Hope" and reality is something entirely different. I got the feeling that they all wanted to rejoice in calm, but also wanted Sin to be fully vanquished if they atoned for their Sins, but it was obvious that their goal wouldn't be achieved because life revolves around Sin, even when not intentional.

It was all what Yunalesca said "False Hope" and the Spirians couldn't be brainwashed enough to not realize that Sin would return, especially after 1000 years of fighting the creature.

Auron definitely knew of Sin returning, but this relates to after his confrontation with Yunalesca, cause why would he wait to hitch a ride on Sin after his death? I agree that he probably never knew about Bevelle's machina because he states "Aah, Yevon finally exposes it's true colors..." but he always had his suspicions throughout the whole game of Yevon, and didn't want to associate with them as well.