Sinizine: It's not that they're STUPID. It's that the things they are doing don't make sense. Not for their characters, and what we've seen of them. It makes no sense for Lori to go after Rick when he quite literally just left like half an hour ago. Watch the episode again. Rick arrives at the bar, and the next scene is Lori begging Daryl to go after him. This means Lori was freaking out before he even arrived. We've never seen her go out of her way to put herself in danger, especially for such a ridiculous reason.
Well, there's the very good possibility that Herschel's daughter is turning into a zombie. Remember how she got grabbed by the stepmom? Collapses with a high fever right after that? Doesn't take a rocket scientist to put two and two together there. That right there is an adequate, but not necessarily smart, reason to go out and get them to hurry back rather than having them sitting there listening to Herschel's sob story.
Here's an example of in character stupidity: T-dog cutting his arm in the season premiere. We've already seen T-dog be a total klutz when he lost the keys to Merle's handcuffs. And zombies were like 10 feet away. Also he named himself T-dog, so he can't be that bright. Or maybe Sophia running away because she's, y'know 10. Contrast that with Lori's decisions this episode, or Andrea suddenly feeling the need to prove herself to the menfolk that she doesn't need to wash dishes when all we've seen of the character shows she's a headstrong, independant person that doesn't give a shit about that type of stuff. And you know what's worse? The characters don't treat the stupid decisions like they are. Andrea was written off with some jokes. Nobody said to Andrea "This is why we kept the guns away from you dumbass." after that obnoxious storyline. Nobody thinks Lori is a stupid idiot in the show except maybe Daryl but he thinks that about everyone.
T-Dog cut his arm on a car when he was trying to hide from the walker herd. That was an accident. Says nothing about him being "stupid". Nor does fumbling with the keys for Merle. What WAS stupid was pretending that he wasn't burning up with fever from infection on that cut.
It's not about everyone suddenly becoming He-men, but remotely competent, in "I can't believe they haven't managed to fall down a mineshaft" way. Or at the very least interesting. Do you honestly want to spend 20 minutes of the next episode with Lori avoiding getting eaten? Stupid people aren't compelling. They aren't sympathetic generally either. But you know we're going to be spending the next two episodes devoted to her rescue. With our characters all super worried. You know why? Because she isn't stupid. Not in the world of the show, and not according to the writers. She just comes off that way because the writers kind of suck.
Glenn is competent. Daryl is competent. Shane is competent. Rick is competent. Maggie is at least semi-pragmatic. Andrea is learning (you simply don't go from 0 to 60 without hitting the speeds in between). Carl is growing up quick. A story with every being able to instantly switch from housewives to zombie hunters is unreasonable and unrealistic. So if you find the characters so stupid and non-compelling, why are you watching the show?
If this was still Darabont directing/producing, your storyline might happen. But he isn't. He's a fan of the gradual buildup storyline from what I've read. The new guy isn't. They can be sympathetic because we all know people like that in our lives.
Oh, and the fact that Robert Kirkman (you know, the guy who created The Walking Dead) is as an Executive Producer on the series makes the progression and character development a bit more palatable.