Flamestrike
Legend
Define frequently.
Ask your DM.
In my games I run, Good necromancers refrain from casting such magic unless its absolutely necessary (and many dont cast it at all). If they start to use it with any regularity (or trivially) I'll change their alignment on the spot (after a warning that the magic they are using is dark, sinister and evil and it makes them feel 'cold and empty inside as the dark magic corrupts your soul' or similar fluff text).
If they do it frequently, Ill change it to evil.