See, I kind of see where you are coming from. But to me, this kind of thing veers a little too close to "the Sith were right all along" style of thinking. The Jedi try to bottle up their emotions, and fail. Palpantine and the Sith don't, and they instead control their emotions and channel them to become more powerful. This is not supported by canon, since almost every Sith happens to be a violent, sadistic killer. Sure, Palpantine can control himself and appear charming, but beneath it all, he is far from emotionally stable.
So, in my opinion, the Sith don't control their emotions and desires. They are controlled by them. They can channel them into something somewhat productive, say using their hate to build the determination it takes to maintain a thousand year plan. But at the end of the day, when all pretense and other factors are stripped away, the Sith only care for themselves. They take what they want, do what they whatever they want because they feel like it. This is, for instance, why they kill people who have mildly irritated them or torture people for fun. When not following some greater plan, they have no filters. They are slaves to their desires.
Also, I'd like to remind you all that Palps died because he gloated and got too emotional. He wanted Luke as his appremtice, and did not kill him wheh he had the chance. When he did decide to kill him, he gloated and tortured Luke, instead of just killing him. Then he was too blinded by his own arrogance and his own triumph that he didn't realize that Vader would turn on him, before it was too late.
