it's obvious that using "tadpole" even for the sake of gaining more power is hurting you.
Is it tho? O_o
I mean, Larian only collects statistics based on the storyline "path of evil"
Serious question ... since i dont remember anymore: Did they even tell us what "patch of evil" is? Or did we just added context on forum afterwards?

Even the companions tell you about it after the next dream. It changes something in you, something "that will never come back". It's not literally "it's hurting you," but it doesn't sound like something good. But I don't think it's necessarily turning us into a monster. Perhaps submission to the absolute and its power affects us in some other way, but it is also bad.
As for the "path of evil", it seems to me that Larian wrote in they statistics "74.85% of you stood with the Tieflings, and 25.15% of you sided with Minthara. Good outweighs evil, it seems."
It's established that True Souls undergo some ritual in the Moonrise Towers and that True Souls are just lieutenants who follow orders, not the real leaders of the cult. If True Souls are 'made' in the Moonrise Towers, then it's obvious there is some high ranking cult member who either knows some useful information about origins of the tadpole, Absolute or the initiation process. The cult members are kept in the dark, but the cult leadership knows both about the tadpole (thats why they told True Souls in the Act I to kill survivors from the crash) and the githyanki weapon (they ordered its recovery).
Right. But we can go to Moon Towers ourselves, we don't need to help the goblins for this. This is the irony. We can go to their "boss" by simply tricking everyone in our path or using a tadpole. We have no reasonable reason to help Minthara.
Later, she can help you, if you persuade her, or she attacks you and you just kill her, which makes the situation even more stupid. In a critical situation, Tav does not have time to help Minthara, and has no good reasons. It doesn't offer you anything in return initially, it doesn't entice you. Another thing is that Halsin immediately promises to help in Moon Towers, even before you help druids or tieflings. Important! What does he tell you about the Moon Towers while still in 'jail', so you can already go to the Moon Towers from there, regardless of the situation with Tieflings.
If we help the Tieflings and druids, Halsin promises to come with us, but Minthara says "attack with me" and promises nothing but "the reward of the absolute". These are empty words, we don't even know what it's about, we just pretend to know.