During an interview earlier today, The Walking Dead's Dallas Roberts--who plays Milton the Woodbury scientist on the hit zombie drama--was asked one of the key questions of this season: Why do fans hate Andrea so much?
His answer was well-considered, and worth repeating:
When my lady and I sit down and watch TV, I find she gets annoyed at characters because they don’t do what she would do in the situation. I’m always like, “Well, she has to do that because that’s what the story is.” Yes, it’s annoying that Hamlet doesn’t kill his stepfather ten minutes into the play, but if he did kill his stepfather ten minutes into the play there wouldn’t be a play. He has to be annoying, if you will, and not do what would be the thing to do. I just chalk it up to people experiencing a story and going, “I wouldn’t do that,” or, “I want this character to do something that this character isn’t doing.” I guess that’s sort of the fun, people get to play along, even if it annoys them.
Of course, there are other reasons that fans have expectations of the character; in the comic book source material, she's a strong, smart and indispensable part of Rick's group of survivors, and very little of that character is on display in the AMC television adaptation, where Andrea is generally seen as weak-willed and attracted to powerful, damaged men.