I'm going to start this off with something I've noticed with these type of movies. Whenever there's a strong female lead(s) you'll find that most of the negative reviews come from men. I laugh every time I read their reviews. They complain that it's another girl hates guys movie. I bet they enjoy the movies where it's a man killing women.... But hating men is not even the point with this movie. Stop reading if you don't want the movie spoiled.
To me, the point of the movie IS revenge but also twisted loyalty and obsession. They don't kill random people on the street, they killed people that hurt Shae whether by indifference or directly. The guy that assaulted her, and her ex were two people that hurt Shae physically. Even if the ex didn't physically hurt her, he definitely did emotionally. The friends of the rapist seemed indifferent or just plain in the way. The cop was definitely a jerk to Shae. The last guy was killed because he was getting in the way and the sociopath was so obsessed that's all she could see. All of the men that died weren't innocent in regards to hurting Shae. None of them really deserved it except maybe the rapist. That's just my personal opinion. The one thing I didn't like was the absence of cops and the disappearing bodies. What did they do with the bodies? How were they not arrested? In the real world they would have been caught pretty quickly. Forensics would have been their downfall. That's my only complaint. I don't regret watching it, don't know if I'll watch it again, but would definitely recommend it to my female friends.