Alison was the one that taught Hanna the worst possible way to get hot, using behavior mod techniques that would make Cesar Milan proud, to make her the next Alison.
Alison outed Emily in the greediest possible way, tempting her out onto a limb and then jouncing it with all her might, and now that Maya's replaced Alison (maybe literally, somehow, if you keep an eye on those blonde wigs) and been taken away in turn Emily is basically nonfunctional, just like Ali would want.
Allison needled Spencer about Ian while sleeping with him, which turned the entire Hastings household radioactive and brought the Spencer/Melissa war to a deadly pitch that is still knocking out casualties left and right.
She even managed to get poor Jenna blinded, in a way that had to do with the parts of her own relationship with Jenna's brother we still don't entirely understand.
And what it comes down to is what both Caleb and Hanna were saying, in their different ways: Just because you have all the power in the world it doesn't make you feel any more powerful when you can't use it. The difference between oil or money and being a human commodity is that oil or money don't feel like shit about it. Ask any drug dealer the number one worst thing about their job and they'll tell you: I have all this money, and I can't spend any of it.
All Alison really did was show them just enough of the prisons they're in that they couldn't ignore it anymore. And then forgot to give them the key.