Boromir was the only member of the Fellowship who tried to take the ring. He was vain and entitled, believing that he alone, of the Fellowship, was worthy of the ring. He was a thief and a traitor.
Boromir was a Lord of Gondor, and he wanted everyone to know it. “His garments were rich, his cloak was lined with fur, and he had a collar of silver in which a single white stone was set.”
Boromir did not redeem himself. He failed to protect Merry and Pippin from the orcs, who wouldn’t have found the hobbits wandering alone if it weren’t for Boromir’s actions in the first place.
Boromir would not have felt remorse or apologised if he had succeeded in taking the ring; he only did because he was caught. His image was so important to him that his “heroic” death was staged to create sympathy and goodwill so that he would not be remembered through the ages as a thief and a traitor.
Boromir got what he deserved.
Because Jackson didn’t understand/mischaracterized Gimli, quite frankly. Movie Gimli matches the modern fantasy idea of a gruff 'n ruff dwarf fairly well but book Gimli is far more thoughtful.
They knew something bad had happened in Moria in the novels, and they even had a fairly good idea of what it was (the Balrog was called Durin’s Bane for a reason). Gimli held out hope because it was family and his ancestral home but he, and everyone else, knew it was unlikely that they were alive.
Really, it was Gandalf at fault for the whole thing. The others might have thought they understood the risks, but they couldn’t as mortals. Gandalf should have damn well known the Balrog would be awake as Mordor builds its strength again, though you might accuse him of the same flaw as Gimli, simple denial in the face of tragedy.