I never could bring myself to become a cannibal. I just find the idea really repulsive and have only successfully completed Taste of Death once. So I usually just kill everyone in the shrine and let the priest go.
Skyrim is the first game where I find it hard to fully complete a number of the Daedric quests.
I have never completed Vaermina's quest as I felt like too much of an ******* in killing the Dunmer. However, I did complete Mehrunes Dagon's quest because Mehrunes' razor is a good dagger, and it has a pretty nifty sheath. I also haven't finished Boethiah's quest, but that's mostly because I'm rarely able to continue playing a character past level 25 for some odd reason.
Namira's quest is one that I will NEVER complete even on a Bosmer or enthusiastic werewolf. I despise cannibals with a passion (for some reason it's tied to Jade Empire's cannibals, as well as a short horror story I read around the same time involving cannibals), and murder them in every game where they appear (and it's an option). I even murdered the "vampires" in Fallout 3.I even have issues on feeding on humanoid corpses as a werwolf.
It doesn't help that Skyrim's cannibals are vile characters. The shopkeeper mentions that she was going to end up killing and eating her assisstant while blaming his death on the Forsworn. Keep in mind that she claims that her husband died to a Forsworn ambush AND had "great taste". From this we can conclude that she murdered and ate her husband.
The meat merchant is equally vile because he sells human meat to unknowing customers. The dog trainer is the only one that almost gets a pass because he only feeds the meat to guard dogs, but that can make the dogs dangerous even to their owners. Eola, besides wanting to kill a harmless priest of Arkay, was desperate enough to start eating the bodies of the dead. While I suppose one could make the argument that eating (long) dead bodies is better than killing people and eating them, it's still disgusting.
While I would prefer to just kill Eola the first time she talks to you, I prefer to go all the way to the ritual to purge Markarth of cannibals.