The situation with the player being aware of the tadpole while none of the evil people are is such a strange part of the narrative on Larian's part. I think that should be addressed too, so that the player is not signing up with people who know less about their precidament than they themselves do.
I have to agree; this is really stupid, and it makes following the evil path willingly also a stupid move. There is no point looking for help removing a tadpole from people who are tadpole denialists - evil characters are not always insane, they are generally selfish. Selfish means self-preservation is important, and there's nothing to indicate that siding with the goblins will increase your chances of self-preservation.
Why would any evil character wanted to get rid of something that is giving him benefits, especialy if he dont need to yet?
Because they are not brain-dead or insane, and can understand the concept of future negative consequences?
