Land of the Dead/Headscratchers

The sparing of the Zombies and Big Daddy. WHY?
This seems like a curve ball of the biggest order. Riley, before the ending, cared about the people in the town, the town itself and people in general, Jerkass nature aside. But at the end of the film, Big Daddy turns and looks at him, and instead of ridding the world of the threat of tool-using, sky flower-immune zombies, he lets them go, stating "They're just looking for somewhere to go. Bullcrap. They weren't looking for somewhere to go. They're either wild animals that just slaughtered most of your town, or they're thinking people, who just declared war on you and tried to eat every last one of you. Killing the former is putting down a dangerous beast, the latter is ridding yourself of a deadly enemy. Sparing them works in neither account.
 * But neither interpretation is correct. When the zombies started the assault they were only on the verge of regaining a semblance of sentience, and were driven only by the half-understood desire to avenge their brethren killed by Dead Reconing. In the end they've gotten their revenge, and started to understand that there's more to unlife than killing and eating; they see Dead Reconing and hundreds of survivors, but after a moment of hesitation just shrug and move on, deciding that it's no longer important. This was a mutual armstice by the two sides, neither capable or interested in destroying the opposing side any more. The most important reason for sparing the horde however was undoubtedly the hope that they could teach other, feral zombies that they come across, reaching a situation where the undead would no longer be a threat to the remaining living.
 * OP here: And how was Riley supposed to know that? All he saw was that the Stenches(their term for zombie) just killed and ate a whole lot of people. All he saw was Big Daddy look at him, something zombies have done in the previous films before putting on a hostile face when about to attack. There was no armistice. It's not like Riley and Big Daddy went to the bridge and sat at a table to hammer out a treaty or something. They glanced at each other, that was it.
 * Didn't one of the minor characters living in the slums mention something about retaking Fiddler's Green at the end? I think it was the dad whose son was sick and was given medicine by Riley earlier in the film. True, the rich people living in there were zombie chow, but the main surviving cast saw that essentially the entire group living in the slums survived. I think he also cocked a rifle as if ready to go shoot up some zombies, and Riley and his crew were simply more interested in getting out of there for a hopefully less infested place.
 * Basically it's bad writing resulting from the movie's stupid "humans are the real monsters" message, among other stupid viewpoints.

Zombies are sympathetic?
As noted under the YMMV page, while partly due to Darkness-Induced Audience Apathy, there's a very real sense that we're supposed to sympathise with, not the humans, but with the zombies. Seriously, what the heck? Romero's "__ Of The Dead" series have always been somewhat misanthropic, with Humans Are Bastards being as important to the plot as the Zombie Apocalypse, but did anyone else think that this crossed the line to being insufferably preachy about the Humans Are Bastards element?
 * The movie's insufferably preachy on a lot of accounts.