Well, LF, I've already answered this one in another forum posting, but i'll reitterate. Farimir's character got twisted 4 ways from sunday, that's correct, but it did so for several reasons.
#1 Faramir can't appear to be as strong as Aragorn, Aragorn it the main hero of this so only he should be able to fully turn away from the lure of the ring.
#2 Faramir, by dragging Frodo and Sam off to Osgiliath, gets to show us that Sauron is still kicking a** and taking names. We need to show the audience just how much of threat Sauron still is, beyond that of seeing humans waltz into Mordor.
#3 Faramir gives Gollum that extra bit of reason he needs to make Gollum decide to betray Sam and Frodo, which will be seen in return of the King.