Anger is something I've dealt with all my life. As far back as I can remember, when I was wronged in any way, I impulsively wanted to strike back. The vast majority of the time I've been able to hold back. I have a short fuse, but good self-control. Unfortunately, this scenario caused me to internalize that anger, bury it deep until I come to a point where I lash out at those close to me, and at God.
My reason for telling you about my baggage is to explain that anger, and other dark emotions, are nothing to play with. They can provide the illusion of strength. Fear, hate, aggression... give you a rush of power, a power you can harness. It feels good for a while, but it will gradually eat at you. It grants the illusion of energy, while it, in fact, saps it from you.
Yoda said that the Dark Side of the Force is quicker, easier, and more seductive. I would grant him as being right about two of the three. The Dark Side is NOT easier. If anything, it is more difficult. This is because it is harder to cling to your anger. It's much like a pot of water, boiling. The anger boils inside, and the more you try to keep a lid on it, the more pressure that builds up. Until... boom. Your anger and your hatred explode, wrecking your life and everyone in it.
What is the alternative? Letting go. You have to express your emotions in a productive manner, usually through physical activity. Exercise and martial arts are phenomenally useful in releasing your negative emotions so that you can go about your life in peace.
Peace is underrated. Peace, according to the Sith, is a lie. The truth of the matter is peace can be far more powerful than anger, hate, or aggression. It can heal wounds — physical, emotional, and spiritual. It can resolve conflict. It can bring you wisdom. It can set you free.
And that, in my opinion, is the most important part: freedom/liberation. This doesn't mean you cut yourself off from people you love or things you need to accomplish. Rather, this liberation gives you the enlightenment to do exactly what needs to be done.
Anger is not necessarily an evil emotion. Anger, though, is a swift enforcement of perceived justice. Justice is in the hands of the Father. He is the one who enforces the wrath. We should not succumb to anger and strike back, especially when we do not see the bigger picture.
Yet there is a time one is told to strike back with the sword. Remember, the blade should never be ignited unless the order is given to strike. This is being passive. It is not allowing the Dark Forces to influence your submissiveness. Passion though, which is seen to be the opposite, is a strong emotion… yet is still controlled.
With that said, emotion itself is not an evil thing. The mere act, when performed selfishly, can allow evil to slip by. We are so focused on the self that we dwell in a state of inattentiveness. It is a natural state of mind. Yet, if we are under the spiritual influence of the Father, and focus our energy to what matters, one can use passion and emotion to do the unthinkable. This is how people can do incredible things when people's lives are in danger. Saving people from drowning, falling on a grenade... this cannot come from a personal state of mind. It is an act of a greater will.
The best way of seeing it is how Luke Skywalker responded to Darth Vader when his sister, Leia, was threatened. It was a selfless act of passion; dare it be said, anger. When harnessed, it should be able to be turned off within a controllable state. It would be a travesty if we did not show a hint of anger to those who are destroying this world… the evil principalities that are attempting to take over this universe. This should not be ignored.
Attentiveness, without the involvement of the true spirit, still leads to ignorance… or, worse yet, non-action. You only are aware to that which you have been given. Remember this.
Emotions should be given to the Father. That is what prayer and meditation is all about, for it is a natural release. When we do not give these to the Father, and bottle it up inside, we eat ourselves. As Streen said, it's like a boiling pot of water ready to explode. As it boils, it loses water and turns to steam. It is a transfer process which, one performed, cannot return to its original state.