There is also what is known as "vampiric Necromancy", where one consumes the life energy of another to replace depleted essence of their own. Some Necromancers use knowledge of the soul to manipulate the living. Others simply work with the essence of Death itself and may travel to the realm of Death.
Others may also attempt to make themselves able to withstand deeper immersion in the essence of Death, to better wield its ability and to increase understanding. To transcend flesh is this goal.
And yet again there is the type of Divination done with the dead, or medium work (which could be considered a form of Necromancy).
I would say, that with any magic, "good" and "bad" is simply in how one uses their talent and how society percieves this use.