I made a Maormer (darkelf oracle eyes fishskin whitehair) necromancer

He uses corpses from the sea and reefs and costlines. Lots of dead to be found in the deep to pull from. Does not need to kill to obtain bodies. Was trained by the sload to be an emissary for them and the maormer. Is considered a noble and worthy magics in his culture in my headcanon.

Here's a few different ways to explain why a Necromancer might want to be an adventurer that helps people:

-Practicality. Being a criminal closes a lot of doors, being a hero opens a lot of doors. People trust you, you have influence over political figures, etc. Besides, with all of the world ending threats going on, you can be a self-serving person who just realizes they have the power to save the world and do so because "Nirn is where I keep all my stuff".

-A very different perspective of the morality of Necromancy. Some people in Tamriel think Magic, in general, is evil, and they could go on for hours to tell you why they think that, but there are plenty who would refute that with also plenty of reasons. If your character has the perspective that Necromancy is just a tool and not inherently evil, I think that would allow them to have normal motivations for adventuring as other adventurers would. Maybe you personally don't agree with those reasons, even, but your character could.

-Redemption. Maybe they were once led down the dark path of Necromancy and used it for evil purposes. Maybe they had a tragic incident happen in their life, the loss of a loved one, and the Worm Cult, or any other Necromancer cult, led you to believe that you could bring them back if you offered to help them, and went down the slippery slope. Perhaps they gave you a taste of that by bringing their spirit up for a few moments to talk to you, before sending them away and saying that eventually, you could have that power. Eventually, for one reason or another, you feel the Worm Cult crossed a line, or maybe betrayed you, and that could even be why you ended up being sacrificed to Molag Bal by Mannimarco, and now you're on a quest for vengeance and using their own magics against them. Fight fire with fire, and have an insight into the enemy that not many have. And maybe, you even start to have a change of heart down the line.

-Cultural differences. Not necessarily strictly racially-wide, but perhaps tribal-wide cultures of where your character grew up saw Necromancy as not inherently evil, or perhaps even used it. There was that tribe of Nords that that Nord from the Dark Brotherhood came from that were all Werewolves, maybe there's a tribe of some race that took to Necromancy as their focus and that's how you learned it, and you find it strange that other people think it's evil.