Why necromancy even have to be evil? It could be art of creation automatic constructs for manual labor, while living people learn and trying to make their lives even better. And give your body after death for a necromancy construct creation is a honor, a good thing.
"Let's dead work and go to danger, while our living have happy long life. Dead body not a big sacrifice, because soul is who we are". - Well, many authorities will not accept this new philosophy. Kings, Nobles or Churches may make them villians and try to destroy new school of thought, kill scholar and start violence. Other side answer with violance and maybe go too far with it, or among members we find some really evil people, that make thing even worse... Maybe even we will present this rotten apple? They can be bloodlusty, megalomaniac, cruel and aware of it, trying to get power. Maybe not so evil? Maybe, they could be a fanatic, believing in infallibility of this way, maybe in their chosenness... Or just someone in the wrong place, in the wrong time and without a choice, hurt and mentally broken by violence.
Megalomaniac. Poor Madman. Heartbroken.