Frodo and Sam assume, as Faramir also assumes, that anyone they meet in Ithilien and the lands around Mordor will be enemies. Though Ithilien used to belong to Gondor, it’s been corrupted by the enemy, and Faramir can’t believe that simple travelers would be passing through. Frodo’s dedication to protect Gollum, gain his trust, and rehabilitate him as much as possible persists even in danger. Gollum has been loyal to them, and Frodo has adopted him as another of his duties.