MORE: In the comments, Michael points to this WaPo review by Stephen Hunter and says it explains what bothered Dargis. It's a bit of a spoiler, but here it is:
What I like about the film, however, is that as an intellectual tiff, it argues fairly. That is, it doesn't give us an idealized version of "freedom," as off a Norman Rockwell magazine cover in the '40s. No, no, it says: Freedom will be squalid, violent and dangerous. The key moment in the film comes when Carol faces freedom's ultimate challenge, which is defending it. She faces six men who want to take her down and "cure" her. They have totalitarian will and little regard for their own lives. She has a gun. But does she have the will to use it? Very interesting question, not only within the movie but within the world. The movie, at least, has an answer.This makes me think about the book "The Sociopath Next Door," which I've been reading. The sociopath, the author (Martha Stout) tells us, has no conscience and is able to manipulate and harm normal people precisely because they do continually question what they are doing, whether they are wrong, whether they've lost their mind, etc. To wonder if you made the wrong decision then, is to give proof of your humanity. Stout talks about Barbara Graham -- the woman executed for murder portrayed in the movie "I Want to Live" -- whom she characterizes as a sociopath. Graham's last words were "Good people are always so sure they're right," which Stout says is exactly not true. Good people are the ones who are not sure -- as Graham (Stout thinks) knew when she chose them for the purpose of inflicting torment.
Another excellent moment: After making her decision, there's a wonderful scene that finds her in the kitchen as she has a crisis of the spirit: Did she make the right choice? Why was she so sure? Maybe her primal instincts were wrong?
Her ambiguity is the best coda to a movie that really asks the hardest question of all.