The problem with evil paths in games is that they are almost always illogical.
This. 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.
That's... Pretty much it. I tried an evil playthrough a couple times but all my evil characters bounced off it because they have absolutely no reason to think siding with the goblins is in any way beneficial to them. As far as your character knows the tadpole is a ticking time bomb, and while it may seem to have a strangely long timer it will inevitably kill you.
No evil character would side with the Absolute as it is written right now. Even the Joker, the most iconic example of Chaotic Evil out there, would be trying to get the tadpole out because if he dies to the tadpole he can't make Batman kill him instead.
So the only logical path forward becomes Halsin. Good or evil it doesn't matter. As long as the player has reason to suspect their life is in danger an evil character will side with whoever can ensure their survival.