The trick from a role-playing perspective is to create an Alternate Morality (I reject your Morality, and substitute my own!) in which things like Cannibalism, and Necromancy are not unethical, and may be seen as an honor. Malakath is a Daedric prince, essentually a Devil just like Mehrunes Dagon, and Boethea, but patron of the Outcast, and Betrayed. Vengance would probably be all right in His book, so one way to lampshade it is by retconning that certain people, and factions are outside this Morality. It's the Elves' fault, they cast us out, hunted us, and turned the other peoples against us, so they don't deserve mercy.
HE also respects Strength, and expects his followers/Heralds to live by this concept. This is Honor in Orismer society, just as the Catholics decry Suicide as Sin, while the Shinto codify it into the society including the situations where it is Mandatory to save face, and maintain the honor of the ancestors.
In some cultures, Cannibalism may be an Honor, reserved for kinsmen so they can live on in some way with their progeny, and also honored Enemies to take some of their strength. Likewise, Necromancy (In a fantasy setting) may locally be seen as an Honor reserved for the high class (Possibly a holdover from before the Orismer split from the Aldmer?) to make them immortal. Of course, if you have the ability, body, and need for some spare hands, the lesser temporary resurrection can also be useful, but such a society would differentiate between mindless Zombies, and the High Revenants who can think, interact, and even rule, indefinitely.
Necromancy is not generally associated with Malakath, nor Orisinium, however, which can be explained by being from a splinter faction, or sub-sect of Orcs, or mixed race believers. Perhaps you're from Vvardenfeld, or High Rock (Both places with some Orcish immigrants, but a whole lot of Necromancy.) Something like an Arkay Death Cult, once led by a powerful Necromancer, Lich King, or Master Vampire. Everyone else might consider you Evil (If they ever heard of you, did I mention it's probably a Secret Society?) but you were raised on this, as well as all the Rationales, and secondhand delusions from the charismatic leader.