Sages like Durvasa and Viswamitra used their anger as a tool to intensify their energies. It is not that they were angry at anything; they were simply angry. Since anger is a very intense emotion, it is possible to use one's anger as another tool in one's sadhana. And, as @srimannarayanakv points out in their answer, these instances of wrathful cursing are few and far between, but they are what stick in our memory whenever we think of Durvasa or Viswamitra. The rest of the time, they were surely beings of great equanimity and wisdom.
It is possible that you are looking upon the actions of these sages from a moralistic viewpoint, which is simply not relevant for them since they are coming from a pure energy state, in this case, pure anger. Applying a moralistic lens over their actions would be to do them a disservice.
There are some sages who also use their anger as a kind of defense mechanism — to keep away all but the most intense of seekers. Sadhguru Sri Brahma was one such yogi of the last century — apparently, he would always be in an intense state of anger; again, not at any issue or any person, just simply angry. And common people would flee from him in terror, because such was the intensity around him.
So, yes, Durvasa and Viswamitra and others like them were no doubt true sages, and great ones at that.
Source: Anger is Intensity — Sadhguru Jaggi Vasudev - video extract from the Isha Yoga 7 day program held in Atlanta, Georgia USA in 2003
Seeker: In our Indian tradition, these great seers like Viswamitra, they were all angry people and they could never get control of their anger. So, what is the nature of this anger that afflicts us?
Sadhguru: See, you must understand, anger is intensity. Please look at your life and see, probably anger is the most intense moment many of you have known. Yes? Is it so? <crowd murmurs in affirmation>
Anger is intensity. Intensity is good. But, because you are attaching an emotion to it, which is becoming misery, which is destructive... Both, to yourself and to what's around you, which is the problem... If you can remain as intense as a Vishwamitra, very calm, that would be fantastic, isn't it?
But, right now, he has worked through his anger, he has worked with his anger, used anger as a tool always to rev himself up to high intensities. So, once in a way, because it is... because his intensity is attached to a certain emotion, it spills over. Whatever the negative stories that you hear about them are little spillovers. Rest of the time, they were wonderful sages, you know?
But, in your life, every day you are doing wonderful things to everybody. Just one day, you stabbed somebody, okay? All your life people will remember you as just that man who stabbed somebody, isn't it? Every day you did so many wonderful things to people. But that's not the point, you stabbed one man one day, that is what will stick with you, always. Because, people's minds are so focussed on the negative. They enjoy the negative, because it's like them. Laughs. Stabbing is something that they always wanted to do but they never did. Because it's a wrong thing to do, that's the only thing that stopped them, their morality, not their humanity. Yes?
So, you don't want to stab anybody out of your humanity, that will be wonderful. But you don't want to stab anybody because it's a wrong thing to do, that's a horrible way to live. Yes or no? Most people don't stab anybody because it's a wrong thing to do, not because their humanity doesn't allow them to do such things. So, these Vishwamitras and Durvasas and others, they flew into a rage because they don't come from morality. They just come from pure energy states. Seething anger. Shiva himself, you know? Shiva is fury, all the time.
You should have... laughs. Yesterday they showed you a picture of one person Sadhguru Sri Brahma? A black and white picture that was in the telefilm, did you notice that? No? He was like this, all the time fury. Not about anything, not angry with anybody, simply angry. Laughs. Just so angry. All the time angry. Not with anybody, not about any issue, just simply pure anger. Because he doesn't want to get entangled with love and compassion and all this stuff, he keeps himself angry. So only people who can look beyond that can be with him. Other, you know, namby-pamby people, they cannot be with him. Only intense seekers can go to him. This is a defense system, okay? This is a defense mechanism.
Now... laughs I shouldn't be saying too many things about myself. Now I am here in a program like this, I am very pleasant. At least, okay, reasonably pleasant. <crowd laughs> You must see me in other programs, I won't be so. You will see a completely different man if you see me in advanced programs. First two basic programs I am one way. People come into advanced programs, suddenly they find, "Oh, we came here thinking he is such a wonderful man, and here he is!"
I am not going into anger, I am not the angry kind. But, my intensity will be such that you will be afraid to come anywhere near me. If I am talking you can come, if I sit quietly... even now if I sit quietly, people won't come anywhere 100 feet around me, because it's... it terrifies them. I don't say anything, I don't ever shout at anybody, nor even, you know, raise my voice. If I just sit quietly, they'll just all stay away. This is not because I've become like a bomb, or damaging, or hurting, or anything. It's just the intensity, people can't take it. Sun is life nourishing, isn't it? But can you go close to it? So, it's just the sheer intensity of it.
So, without intensity there is no transcendence. The reason why people do not transcend is, they don't do anything intensely in their lives. All these moralistic teachings and these pacifying religions have made people all... neither this nor that. Just trying to be good, trying to be good, trying to be good... No intensity. Without intensity, there will never be any transcendence.
So, easiest way to become intense is to become angry. Laughs. But it's very negative. If you know how to be angry, not about anything or anybody, simply angry... Just try and see, just experiment one day and see, if you just know how to be simply angry. No object should be there, no purpose should be there to your anger. Simple anger. You will see, you will become very meditative. Effortlessly. Because once intensity comes, transcendence naturally comes.
So, they have been very badly misunderstood. They have been judged by moralistic societies, not understanding who they were.
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