If a mechanic's purpose is to act as a temptation and resisting that temptation gets you an equal yet opposite mechanic as a reward it kind of undermines the function of the mechanic in the first place.
That isn't to say there can't be a sort of narrative balance between using it and not using it. Not using it just needs to reward the player in less tangible, measurable ways.
The easiest example is that to maximize your tadpole powers you need to need to harvest True Souls. This will lead you to kill your companions and probably bring you at odds with the Absolute anyway, as you'd want to harvest their True Souls too. You'll burn bridges on both sides of the conflict and likely end up alone against the world.
Or maybe you go halfsies and join the Absolute to harvest the tadpoles of the good companions to strengthen yourself and your evil-aligned companions. But now you're surrounded by power-hungry monsters who are proven willing to turn on their allies. You're also in the organization with the most access and knowledge of the tadpoles, but you're also at odds with all of Baldur's Gate with only the might of one insane cult to fight your war.
Or you resist the tadpole and maintain strong connections to your allies. Maybe you get betrayed by a few of the most evil companions, but you have total trust in the ones who've stuck around and have formed a powerful alliance with various NPC factions that are all uniting to protect Baldur's Gate from The Absolute. You might have less personal power by the end of the story than the first two options but narratively you're much stronger, with loyal allies and armies of good at your back.
