You know, the entry requirements for the Corps used to be "utterly honest and utterly fearless," even as late as the mid-80's "Emerald Dawn". This seems to have fallen by the wayside in recent interpretations of the mythos, focusing on the "utterly fearless" part of the equation.
When Sinestro's fall is told in the movie "First Flight", and when it is retconned in Geoff Johns comic issues, Sinestro was a corrupt person driven by a lust for power and control. By contrast, when Giffen and Jones retold Sinestro's fall in Emerald Dawn 2, he was a good man, doing what he honestly felt was best for his sector. His fall from grace came not from personal moral failing, but was literally the fault of the Guardians' arbitrary definition and enforcement of "moral right" based on a majority opinion of other lanterns. Acting upon this reasoning, Sinestro's actions as villain become based on a desire to do what's right - as he defines it.
I always found it curious that the Guardians were unable to wield the rings themselves. Appa Ali Apsa boasted that it was because their own personal power was already greater than that of the rings, but Ganthet confided to Hal Jordan that the rings were designed to seek out wielders based on abilities that the Guardians did not possess - meaning no Guardian was utterly fearless, or utterly honest - a curious group to set themselves in a position to decide what is best for the universe!
Guy Gardner was always my favorite example of this ideal (pre-Johns). As a ring-wielder, Gardner was not only utterly fearless and self-sacrificing, he was also utterly honest, and it was this trait which Giffen and Jones played upon as Gardner's chief character trait in the 90's Green Lantern and Justice League International/America. Although abrasive, although never really liked, the League, including Batman (portrayed as generally distrustful in this series), always trusted Guy to do what was right and not to betray them or act against their best interests.
Even more than the ring constructs and unlimited potential of the emerald energy, this concept of honest and fearless was always my favorite thing about the Green Lantern character, because it defined them in very specific ways that should make for some fantastic super-hero action. For example, "utterly fearless" means not only that he is not personally afraid of harm, but also that his worldview is unshakable (no fear of moral compromise), that new tasks are met as challenges to be overcome (no fear of failure), and that the safety of others is not a leverage point against him (no fear of being unable to protect them). "Utterly honest" means the character is completely trustworthy, abides by the law where it applies to him, and acts out of moral certitude. With these parameters absolutely defined, we have great potential for character-driven stories. Some of the best in this stripe were done by Dennis O'Neil in the 70's and by Gerard Jones in the 90's at complete opposite ends of the storytelling spectrum. O'Neil's stories were hard-bitten social commentary. Jones wrote light-hearted adventure. I like it.