RA92 said:
I Am Legend would have been so much better if it had the original book's ending.
Like the movie, Neville killed a lot of the infected and tried to find a cure. The difference is that in the book the infected were slowly trying to overcome their disease and build a new society. The protagonist is executed by this new society in the end, when he realizes that he, a remnant of old humanity, is now a legend to the new race born of the infection. He recognises that their desire to kill him is not something he can condemn. As he dies, he thinks: "[I am] a new superstition entering the unassailable fortress of forever. I am legend."
There actually was a different ending to the movie which was way better than the one we got. The only problem was that idiot focus groups were idiots and whined about the ending not being action-y enough. It wasn't exactly the same as the book ending you described but it was closer and way better than the movie ending we got.
Basically the one Zombie that got kidnapped by Neville to try and get a cure from was the wife of one of the Zombie Dudes. So most of the time they were just trying to save one of their own. It also shows that they are getting more intelligent than first assumed and therefore hints a bit about them maybe building a society on their own.
You can watch that ending on youtube, it's from the directors cut. So my point is: You can't blame the directors 100% on the ending. They originally did made a good one and were kinda forced to change it.