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.
That specific case of his action during the Revan novel is actually not him using both sides of the Force. People misunderstand what actually happened. That event has distinct similarities to a brief moment of Oneness with the Force. A moment of clarity in the Force where you unleash immense power. Similar to Jacen Solo's moment. However, that moment seems to be a one time deal. As both Revan and Jacen have not, to my recollection, done so a second time.