Ali: I made you Spencer. I made all of you. Before me you were just some goody goody in plaid who did whatever mommy and daddy told her to.
Spencer: You're so full of yourself. You think that just because you brought us together you can treat us like puppets?
Ali: But you are. Don't you see that? You don't exist without me.
She trades in secrets like they were the most valuable things on the planet, and in her hands they really are decent weapons, keeping everyone else around her on their toes and doing her bidding. Her friends frequently remark on how ruthless she was. She's also cunning. After police arrive at a fraternity party that she and her friends crashed, instead of trying to sneak away in an attempt to avoid getting caught for underage drinking, she walks right up to a policeman and asks him to take them home. She explains her chutzpah thusly: "The bolder the move the less anybody questions it."
She's manipulative, but everyone still loves her, which is a dynamic that is actually explored in an interesting way on the show. Even after all that her associates learn all sorts of bad facts about her after her disappearance (death?), they still self-confessedly love her and admit that their lives will always bear her imprint.
In rehearsing a school play, "The Bad Seed," her friends are discussing some of the moral issues in the play, including the question of whether people are born bad or made bad. One of the characters remarks, exasperatedly, "I'm having a hard time figuring out who's evil and who's just naughty." The same goes for the show. It's not clear who anybody really is and the characters that are the most well-meaning are often the characters who do the most dastardly deeds -- much worse than the actual sociopath herself. So in that way it is true to life. But it also makes us question, should people get a pass because they're being naughty rather than evil?