frodo was both the weakest and strongest person in the Trilogy?

[Joy]

In some ways I agree with you. Sam is the stongest of the two hobbits. As some one stated before, that LotR was Sam's tale, it ended with him saying

Well, I'm back

It was a story of his growth, his undying love and friendship to Frodo.

As far as Frodo being weak because he couldn't bring himself to kill to defend the Shire, I do not see this. The reason he did not want to kill was because of mercy and pity. He had learned pity through Gollum. Remember the line that Gandalf said to Frodo?

Frodo: He deserves death.
Gandalf: Deserves it! I daresay he does. Many that live deserve death. And some that die deserve life. Can you give it to them? Then do not be too eager to deal out death in judgement. For even the very wise cannot see all ends.

It takes a stronger person to stay the hand in mercy than it takes to strike with the hand.