Well, I share the same opinion, but not everyone is the same. Some want to enjoy an evil character/romance expecting to have something like a "romance" with evil characters. Until they realize that they will not have any sort of good endings and start blaming the developers. It happened in some games and ppl still think evil path, etc is more interesting which is nice to have this choice. So, let them try and see how exactly Evil is. Ad I hope Larian can make sure the Evil path has some very nasty ending/consequences, especially for "romances".
Considering the original BG2 game doesn't have a bad ending for an evil main character, and you can become an evil god feared by many, I doubt that. I suspect BG3 will follow a similar route, since the premise is somewhat similar: accepting or refusing the evil power, with the difference that in BG2 the evil power came from the divine heritage of the main character.
edit: Another similar game (or rather expansion) is Mask of the Betrayer. I've found the evil ending was better than the good one there.
