Doesn't mean they should have to accept you though. If a faction doesn't want you to join or wants to kill you you shouldn't be able to join them.
This is true, but then Larian need to show an explanatory cast scene and a few dialogues before the druids attack. So far, it looks like the player has not had the opportunity to be persistent enough to ask to become their friend, and they do not explain their hostility after the main character helped them.
Remember Kaghas speech when you try to save the child. You are an outsider, a threat. You must be removed.
They will explain to you, that wolfs will not ask an intruder why s/he is here or tell them to leave - they will attack.
Likewise, they need to protect the grove (and the greater nature) from you, because you are not a Shadow Druid.
You have more success to convince a lolthsworn mother matron that a surface male should be given equal standing to her, than to convince a shadow druid to give people a chance.
Too much of this is the very core of the shadow druid ideology, meaning that such a derivation of ther usual m.o. would make them stop being shadow druids and turn them into just bitter, "normal" druids.
And that is putting aside that your characters are turning into aberrations and thus msot druids would probably kill you anyways.
Partly to safe you and partly to preserve nature.
