I think our society is obsessed with forgiving ourselves for the horrible things we do. We judge ourselves by our intentions, while we judge others by their actions. This movie plays on this, and perpetuates this very selfish way of thinking.
This is why Rachel is scripted as a "good protagonist," when in fact she's a selfish, and entitled covert narcissist.
Dex is the worst character in the movie, the "innocent" stud who never has to take accountability for his own actions, with everyone babying him. Poor frat boy with a mansion. It will be one heck of a divorce, once they drain each other completely.
Darcy is honest, and true to herself, she's the feminist figure, and the script seems to suggest we should hate her. I think it says a lot about the movie that we are told to hate the woman who stands in her truth and is a faithful friend to other women.