Now, Aragorn never actually specifically told Frodo to leave the quest. Of course not! And you can't really say that these were stupid changes. The elves in Helm's Deep show that they actually care about the fate of men, and Aragorn telling Frodo to leave shows that Aragorn wants to help Frodo. The forest was being overrun by Uruk-Hai only to kill Frodo! And, besides. You can't say that all of the things Jackson changed were for the worse. I, for one, am very happy that Tom Bombadil didn't make the cut.