Chosen answer:Virtually everyone was vulnerable to the Ring's power to some extent, even Frodo Baggins. Frodo's purity of heart and incorruptibility made him the least affected by the Ring and made him the only logical choice to actually carry it for the duration of the mission; but EVERYBODY was vulnerable to its seductive power, some just more so than others.
But prior when the Fellowship was formed, he was tempted by the ring. He even tried to convince the council that bring the ring to Gondor would destroy Sauron. So why did Gandalf or Elrond accepts Boromir as a member of the Fellowship?
Well, Boromir's younger brother, Faramir, would probably have been a better choice for the Fellowship, if he had been available. But Faramir wasn't available and Boromir was. Boromir also wasn't actually "chosen" for the Fellowship, he simply went along out of loyalty to Aragorn. Gandalf and Elrond may have suspected Boromir's weakness (possibly even as a threat to the Fellowship), but Boromir was a seasoned warrior whose skills in battle would be valuable on this incredibly dangerous mission. Also, you may recall that Boromir wasn't even nearly as weak or unbalanced in the actual Tolkein story; rather, director Peter Jackson made Boromir more of a loose cannon in the film, which is not how he was portrayed in the book. In other words, Jackson wanted an even more unbalanced element threatening the Fellowship from within, so he amplified Boromir's weaknesses.
Chosen answer: Virtually everyone was vulnerable to the Ring's power to some extent, even Frodo Baggins. Frodo's purity of heart and incorruptibility made him the least affected by the Ring and made him the only logical choice to actually carry it for the duration of the mission; but EVERYBODY was vulnerable to its seductive power, some just more so than others.
Charles Austin Miller
But prior when the Fellowship was formed, he was tempted by the ring. He even tried to convince the council that bring the ring to Gondor would destroy Sauron. So why did Gandalf or Elrond accepts Boromir as a member of the Fellowship?
DFirst1
Well, Boromir's younger brother, Faramir, would probably have been a better choice for the Fellowship, if he had been available. But Faramir wasn't available and Boromir was. Boromir also wasn't actually "chosen" for the Fellowship, he simply went along out of loyalty to Aragorn. Gandalf and Elrond may have suspected Boromir's weakness (possibly even as a threat to the Fellowship), but Boromir was a seasoned warrior whose skills in battle would be valuable on this incredibly dangerous mission. Also, you may recall that Boromir wasn't even nearly as weak or unbalanced in the actual Tolkein story; rather, director Peter Jackson made Boromir more of a loose cannon in the film, which is not how he was portrayed in the book. In other words, Jackson wanted an even more unbalanced element threatening the Fellowship from within, so he amplified Boromir's weaknesses.
Charles Austin Miller