Jedi and Sith are more of the Order vs Chaos conflict than Good vs Evil.
Jedi are evil in their zealousness. Total Order is as evil as Total Chaos.
Both Sith and Jedi use the conflict as sublimation.
Without Sith - Jedi would become Control Freaks.
Without Jedi - Sith would destroy all life.
So they kill each other as a form of sublimation.