1. Nettie only kills you, if you are really bad. She uses that as a last resort, when you don't work with her at all, because she and Halsin where just attacked by a tadpoled person and she is afraid, you might attack the grove. She is doing exactly, what most cautious people would do in her situation.
2. Freeing Halsin doesn't require killing goblin children at all. Those two never died in my playthrough - that is entirely your decision, if they die. Helping Minthara kills children though, without any chance otherwise.
3. Those goblins, that are not hostile, just attacked people in the wilderness, killed and roasted a dwarf and burnt down an inn, killing a lot of innocents.
So yeah, you were saying about siding with Minthara is not evil?
Why should I work with her? I don't know her, she is a druid from the grove, a lot of them already were not very nice to me, and they want to get rid of the thiefling refugees. So I should just trust her blindly with my tadpole problem? Or the artifact? You know, the thing everyone and their mothers are looking for?
It's your descision to not trust her, but then you have to bear the consequences. You are mean, she is mean - fair for everyone. But don't put it on her. If this is enough to excuse slaughtering kids in order to get Minthara - have at it. But don't pretend it is not evil, what you are doing.
And not all druids are happy with what Kagha does - in fact, if you take the time to talk to them, most actually want kagha to stop the ritual and casting the tieflings out.
Oh, and by the time, you usually meet up with Nattie, you don't know at all that the artifact is special, so you are metagaming right now. And the reason you are coming to the druid grove in the first place is to seek help, otehrwise, you don't have any reason to be there and meet Nattie. People are pointing you to her, because you asked for help.
