But the point is that Revan DID do it. You can't tell us not to say that when it is in direct relation to what you are talking about. The alignment system is a game mechanic and isn't the best example but on Dromund Kaas Revan was able to draw on both light and dark. Just because they draw on different emotions does not mean that a person cannot experience these different emotions. Remember that Revan is a very special case. He lived two completely different lives.
Someone can experience these emotions, but not at the same time. To be at peace and full of rage would drive someone mad.
The Voss don't do this, they are naturally gifted with raw
force Energies. Revan didnt have raw force, an example of raw force is Galen Marek or Kyp Durron who friggin exploded with energies without any control. There is a huge difference between those guys and Revan or Vader, and I sincerely hope you see that.