The only angles to align with the mind flayers/absolute I can think of are:
1)Delusional PC, that believe the parasite lunching on his/her brain and the mindflayers have his/her best interests at heart
or
2)Suicide cultist. Selfless/self-erasing PC that assert the renewal of the mind flayer empire as the absolute truth of his/her desire. To such a PC slavery to the mind flayers, and ultimately, death by ceremorphosis, functions as a goal in itself that transcends any personal gain, self-preservation and other "selfish" motives.
I'm not really interested in either RP option.
i like this one. and makes more sense since your looking at it not through good vs evil, reward vs. no reward but another deeper issue.
a. You need Halsin not because he's a poweful fighter, with the ability to slay all, you need him because you want a good healer. Why would you care about his proficiency in a fight? You aren't looking to recruit him as a merc, you want him to heal you.
And i don't understand why you assume 'goody thow shoes' can't be manipulated. Plenty of good peeps get manipulated, if anything manipulating a good person would be easier since they're more likely to believe the shit you say.
b. But when you ask them for help, they don't help! They offer you absolutely nothing usefull -> making them basically useless to you. SO by your logic, you wouldn't want to ally with them, you'd want to kill/ torture/ maim the goblin leaders.
c. But how do you know that they know? From all the convos you have with them they don't give you any rational explanation. No new info. Just a bunch of 'this is the will of the Absolute, i was chosen, blah blah'
d. You don't need to be good to want to get rid of the tadpole. You can be evil and see this tadpole as an inconvenience you want removed at all cost. But that's not the point. When you talk to them and join their side, they don't offer you a way to master your power, unless, again, i missed that convo.
They give you no explanation, no information, no new skill, no new powers. They give you nothing. As an evil char.. why would you waste your time on something that doesn't benefit you at all?
Unless of course you are evil for the sake of evil.
A. Looking at what you've seen druids do. A fairly common druid shape shifted into a bear, if you killed Kadga you'd see her as well shape shift, fought Nettie shapeshift. All these forms are from druids that can't help you, because their not strong enough. You yourself (believe, may believe) that you can take out some pesky goblins, you just did right before entering the grove, and did so easily. your character (may know powerful enough to remove the tadpole) druids are a force of a nature even those focused on healing are nasty in a fight. If Halsin is a strong enough Druid to remove this tadpole he should also be able to protect himself from simple things like goblins, or escape. He didn't so one can draw the conclusion he isn't really all that powerful. That he got captured alone shows he's not stronger then the goblins, and who leads the goblins, the strongest. Talking with certain Npc lets you know information that comes into play into another conclussion (if you didn't get this, or any of the others then it wouldn't come into play from characters stand point.) Goody two shoes can be manipulated but again if he is strong enough to remove this tadpole, he may very well be smart enough to avoid your manipulation (can be enhanced if you fail/failed to persuade Kadga and/or nettie. If your not able to then you can draw a conclusion that he is smarter and less likely to be manipulated by you), or figure out your manipulating him at the wrong time. Manipulating people isn't a given you don't want them to figure it out at the wrong time, especially those that are powerful, and you yourself haven't come into your power yet. It's the before stated Risk to Reward. The risk is very high that manipulation will be found out, by Halsin in this case, and if you put him back in his grove (a thing that enhances druids powers) then you've not only given him his seat of power back, but followers, lost the chance to remove a powerful enemy before they suspected you, gave Heros in the location a safe harbor to work out of. So manipulating Halsin though rewards you with removal or may reward you with removal of tadpole. has just given power to your enemies Which do o moral code good people are, especially Heros, and Halsin is probably one of those types to hunt evil.
B. If they prove useless to you, then as an evil character they are useless, but they have to prove it. Again this goes to you having to prove to them as well. They are evil you have to prove to them your useful. So you have to do what they want you to, again they are evil. Halsin helps you because you rescue him, proving to him (wether or not it's true your useful, and good). This is the basic thing in quests, proof. If you fail at a quest you've proven you can't do it, and don't get a reward. If you complete the quest you get the reward. So for Halsin you got a quest to rescue him, you complete it he heals you or attempts to. If you don't rescue him he doesn't help. Much like if you don't do what the leaders want they don't help.
C. You don't straight up, you do know (if you get the conversation), they are powerful, and have a powerful healer. Again the captured Halsin, are making lives miserable to those behind a fortification enough that the druids are preparing a ritual to protect them. Meaning the druids are afraid of this group even with their magic, and walls. In order for new things to open up you have to follow them to completion. If you don't follow to completion no matter if it's good or evil you won't know. Thats why theres no new info. Halsins quest started back at the Grove when you learned of him. If you didn't follow it then there would be no new info. You asked nettie for help, she didn't help she tried to kill you. again had to follow to completion on Netties quests to find that out, and escape.
D. Your right you don't need to be good to do that, and can see it that way good or evil. It may be a missed conversation, but again you won't know until you follow it to completion. It seems that alot of people are not following these quests to completion or are just rushing through without exploring. Then coming here to bemoan this and that imo. I'm merely offering one view, not all my views, that could be why you join goblins, and not Halsin. IMO it seems people expect to be welcomed like they were in the grove by evil people when they show up, or to not follow the goblins path because it's longer. Instead choosing the quick and easy path which is neutral since your siding with good (meaning you have no real feelings towards good and evil) vs. chosing evil, which may bring about more power for your character, and rid you of someone that will pose a threat in the future. (being halsin, Harpers, and other good people that stroll by Halsin who will heal them, feed them, maybe even supply them since there is a trader in the grove.)
As an evil character why would you help good? By helping Halsin you give everyone that is good and comes by (much like the refugees) a place to stock up, heal, plan, safety, security. Since you are evil that includes those coming after you, or will want to come after you. Unless you plan on leaving and never returning to this part of the country. Which may very well happen, yet anyone in the future coming through here to hunt you down can stop by the grove. Find out you'd been there where you were headed (or direction) stock up, heal up, and be on there way unmolested by the goblins. Region turns stable making it harder for evil to act including you! Because good guys stick together, bad guys don't for very long.
If you find the leaders after completing their quests to be useless, you may just leave and go look for the creche. In that scenerio you can always come back, maybe take over, start a new cult, whatever. yet there won't be for a while a druid grove to stock up heros, offer shelter to refugees, a powerful healer to heal good heros, etc. Even heros coming through are going to have to contend with goblins, and maybe even the leaders. If the heros win good, if the leaders wins good. How is that good because either way a potential rival is done away with, and one or the other is weakened. Hero wins goblins scatter you can manipulate the goblins into working for you, slowly building up your own goblin army, in a region that has been unstable. Region still unstable easier to work in if thats your desire. hero continues to work in region or believes threat gone.
Again all this is just theory, ways of viewing it that matches one of my characters. Each is thought out from what that character knows, and has found out. Are they the way for your character to go up to you.