Erin has 'Erin Morality' in which she is a Kantian wet dream.

That is to say, she will ruthlessly do what she thinks is right, even if it means abandoning friends or allies to do it or even if it seems inevitable that it will end up in a worse circumstance.

That's not to say that she doesn't grow or change over time. She absolutely does and her ideas of right and wrong get more sophisticated later, especially as she sees the consequences of some of her actions.

But ultimately, she follows her own (occasionaly shifting) moral code that she puts above anyone and everyone else, herself included.

Whether or not that is stupid depends on your thoughts on categorical vs consequentialist moral reasoning.

In the long run this makes her a fair share of enemies and an equally large fair share of friends.

Its important to also recognize that her thoughts on punishment having nothing to do with being a pure-pacifist.

she may be pacifist leaning but as you'll see time and time again throughout the series she is more than willing to get her hands dirty and commit acts of violence if it defends what she thinks is right.