All the evil path really needs are some earlier hints that the tadpole:
1: Isn't an immediate threat to the host's life.
2: Can be controlled and abused to gain powers similar to a mind flayer.
You are kidding right?
Every single character we meet, and we are discuising with is talking about that our tadpole does nothing, and therefore we have time, since its alternet by some strainge magic ...
What more do you need? O_o
You never can be certain, since nobody we met so far have even the slightest idea about what exactly this tadpole is, or what it does ... not even a freaking mind flayer know! -_-
And that is just it ... we are supose to play on chance. Yes, we may turn ... and yes, we may controll it ... remove one option, and it become incredibly stupid.
I mean, if there is a certain way to exploid tadpole, and certainly removing all dangers that are tied to it ... why would no one use it before? Especialy if that process is so common knowledge, so some random guy in middle of nowhere knows about it? :-/