If the goal was to "drive the yankees from our land," both battles were thwarts upon the yankee invasion of that land that halted it and pushed it back. Same goes for Chancellorsville.
But the exposition, the give and take between the characters did not show that. Remember in "Gettysburg" how General Buford said, "we have to hold the high ground or there will be the devil to pay." Characters in a story are artistic constructs (even if they are real people -- Buford apparently did say as much) and they have to move the story forward. General Lee saying, "that's where I met my wife," might be interesting, but it doesn't move the story forward -- it doesn't help Jackson reach his goal. I'd still say that Jackson got a lot of screen time without carrying the weight as the story's protagonist. Here's another example. Remember the Episode II of Star Wars. The one with the baby Darth Vader. Some young friends of mine thought it was a great movie. I asked them, "who was the main character?" They didn't have an answer. How was Jackson's goal (as stated by you) any more valid as the main idea of the film than Lee saying he wanted to defend his home? It's not. As a story, we should be be able to say, "okay, this is how Lee is defending his home." Oh wait, Jackson is the main character. It's tough to have split protagonists, although "buddy" movies are a staple of Hollywood. Witness the success of "Thelma and Louise", the original "Star Trek" crew, the four "Lethal Weapon" movies. But G&G was a hodge podge, a mess.
Walt
Did you even see the movie, Walt? Jackson repeatedly converses with others about the battles, speaking of the need to drive the yankees from their land. He even suggests that no quarter be shown at one point. That was in a dialogue between him and other soldiers about the purpose of their cause.
But you cannot be reasonably expected to comprehend that as you have already decided it is not in the film. As I said, you made that decision not on the film's merits or the presence of a goal in it, but rather on the grounds that you disagreed with that goal.
But if the movie version riled you, Just wait for the DVD. It is my understanding that it has historically known scenes showing blacks in confederate uniforms.