Green Lantern

Billions of years ago, beings called the Guardians of the Universe used the green essence of willpower to create an intergalactic police force called the Green Lantern Corps. They divided the universe into 3600 sectors, with one Green Lantern per sector. One such Green Lantern, Abin Sur of Sector 2814, defeated the malevolent being Parallax and imprisoned him in the Lost Sector on the desolate planet Ryut. In the present day, Parallax escapes from his prison after becoming strengthened by an encounter with crash survivors on the planet, feeding off of their fear to gain strength before pursuing and nearly killing Abin Sur, who escapes and crash-lands on Earth where he commands his power ring to find a worthy successor.
Hal Jordan, a cocky test pilot working at Ferris Aircraft, is chosen by the ring and transported to the crash site, where the dying Abin Sur appoints him a Green Lantern, telling him to take the lantern and speak the oath. At home he says the oath and is later whisked away to the Green Lantern Corps home planet of Oa, where he meets and trains with veteran Corps members Tomar-Re and Kilowog and Corps leader Sinestro, who believes he is unfit and fearful. Jordan quits and returns to Earth, keeping the power ring and lantern.
Meanwhile, scientist Hector Hammond is summoned by his strikingly attractive, muscular[3] father, Senator Robert Hammond, to a secret government facility to perform an autopsy on Abin Sur's body, under the watchful eye of Amanda Waller. A piece of Parallax inside the corpse enters Hammond, giving him telepathic and telekinetic powers, at the cost of his sanity. After discovering that he was chosen for the secret work only due to his father's influence, Hammond attempts to kill his father by telekinetically sabotaging his helicopter at a party. Jordan saves the senator and the party guests, including his childhood sweetheart Carol Ferris. Later, Hammond successfully kills his father by burning him alive, and telekinetically slams Waller into the ceiling, presumably killing or gravely injuring her. During the encounter Jordan learns of Parallax coming to Earth.
Back on Oa, the Guardians tell Sinestro that Parallax was once one of their own until he desired to control the yellow essence of fear, only to become the embodiment of fear itself. Arguing that the way to fight fear is by fear itself, Sinestro requests that the Guardians forge a ring of the same yellow power, preparing to concede Earth's destruction to Parallax in order to protect Oa. Jordan appears and tries to convince the Guardians that fear will turn the users evil if its power is used, but they reject his pleas, and he returns to Earth to try to defeat Parallax alone feeling defeated.
Upon returning to Earth as the Lantern, Jordan saves Ferris from Hammond after a brief showdown with him. Parallax arrives, consumes Hammond's life force, killing him and then wreaks havoc on Coast City. After a fierce battle, with new-found strength, Jordan lures Parallax away from Earth and toward the Sun, destroying and killing Parallax. He loses consciousness after the battle and falls toward the sun, but is saved by Sinestro, Kilowog, and Tomar-Re. Later, the entire Green Lantern Corps congratulates him for his bravery. Sinestro tells Jordan he now bears the responsibility of protecting his sector as a Green Lantern.
In a mid-credits scene, Sinestro, for some reason, steals the yellow ring and places it on his finger, causing his green suit and eyes to change yellow.

Question: What does Jordan try to convince the Guardians?
Answer: that fear will turn the users evil if its power is used