I completely agree on your overall point, but I don't think that "good" aka "Hero" players would not want Astarion or Lae'zel in the party.
Imho their "redemption" plot is fantastic, especially for good characters.
From what I heard that might also be true for Minthara.
Minthara doesn't have a redemption plot, she's just got very compelling writing. For how little they gave her compared to the Origin characters, the quality is just as high as any of them. If only the same could be said of Act 3 Halsin.
More toward the general question of why would a good Tav bother, there's also just a TON of evidence in Act 1 that could reasonably lead any Tav, even the most extreme Lawful Good Tav, toward wanting to investigate her as the leader of the absolute's forces in the region instead of just killing her. If the ultimatum between keeping her or Halsin that made the rounds the last couple weeks made it in, that also poses a VERY fun dilemma for such an extreme Lawful Good roleplay.
But Minthara is not the sole leader of the absolute in the goblin camp. The first one you hear about is probably Gut, already in the druid grove from listening to Sazza, and she will also be the first one you meet when you infiltrate the camp. The second you hear about will be Razglin, as he's talked about in the courtyard from feasting goblins and even praised by captured Volo.
Minthara is the last one you learn about, and I don't even think she is mentrioned before passing the doors of the temple. So, why single her out to investigate the cult ? Of course for the player, she is a much more interesting person to have around than Gut or Razglin. I have no doubt about that. But the reasoning behind WHY she is the one to save, namely to investigate the absolute, is shaky IMO. Well, unless the PC would be a drow or half-drow.
