An over simplification and a rather childish outlook. I would suspect catholic versus protestant to be more accurate.
The Force, this 'space magic', is neither good, nor evil. It simply exists.
The Sith are about emotion. Passion. Freedom. Their code is as follows. Peace is a lie. There is only Passion. Through Passion I gain Strength. Through Strength I gain Power. Through Power I gain Victory. Through Victory my chains are Broken. The Force shall free me.
The Jedi cut off their noses to spite their faces.
There is no emotion, there is peace. There is no ignorance, there is knowledge. There is no passion, there is serenity. There is no chaos, there is harmony. There is no death, there is the Force.
Sentient beings, humans in particular, are emotional creatures. To cut off all emotion is to cripple one's development.
The Jedi lack balance.
However, the Sith have developed to the opposite extreme. Too much emotion allows it to control you, to blind you to what the world is like.
The Sith lack balance. Another of my people would have killed the Ongree, they would have murdered that cult.
Sparing both gives me power. That power is strength. Etc etc. And on day, when I make a move to consolidate power, I will have people who support me.
Besides, if one wanted true power, one must have access to both sides of the Force. The whole is always stronger than the half.