Im not against then but I can understand a different array of Roleplay and player profile being against it as in character motives.
Lets say for example a Paladin, a Paladin of Kelemvor so we can have this grey morality present in their order (I remember back in 3.5 times where the Kelemvor order had both Blackguards and Paladins, they would probably disagree in the force necessary to enforce their god wishes but they were still together in this).
Ok we put this fella in party with a necromancer, what you think would happen? Lets make even better what would happen if you put a blackguard of Kelemvor in this party with the necromancer, just for the sake of having two evil characters together.