The real reason to stop the bad guys: move into their fancy castles to use their comfy beds.
I think that after a year of EA camping everyone in the party, regardless of their alignment, would approve of that move. You know that your heroes have been suffering when they smell a goblin leader's feet and think, "hm, lavender, kind of nice, better than us in any case".
By the time they reach Moonrise Towers, Astarion could lure his companions to the dark side of having thrall/slaves/spawns if he promised to use them to carry warm water for their private baths. Hell, Raphael won't even need to promise to remove the tadpole to get their souls; he'll just dangle a fluffy pillow and clean cutlery in front of their eyes and they will sign whatever he proposes.
