So ... the hag in the swamp. I don't get it.
It's not that the quest isn't amusing. However, why would I go there, even as a good PC?
A good PC, because they encountered some farmers who told them an evil hag had their sister prisoner.
An evil PC, because they hear of a hag and know they command powerful magic.
I have this interesting parasite in my brain, and from what I gathered up to that point, my focus is getting rid of said parasite, because it can turn me into a mindflayer any second now. Why would I then wander of into a swamp to rescue spme maiden, when the intro dialog between the hag and the brothers is uninspiring, to say the least.
Even if it wasn't - why would I spent precious time going there.
Because you are good. If you don't think it is worth your time rescuing someone your character is not good, by the D&D definition of the term.
It really doesn't make sense to me, apart from metagaming in terms of "Look, another area to discover."
Can someone enlighten me?
Such metagaming has always been a feature of D&D in general, and the Baldur's Gate games in particular. See: Larry, Daryll and Daryll.