I'd like to add a nuance to the subject of 'nafs' by sharing this quote from an Indonesian teacher and mystic (Muhammad Subuh Sumohadiwidjojo) who uses the same term 'nafsu' to denote the lower forces that we need in order to live in this world. In his experience nafsu are indeed dangerous, but are only a threat to human beings if they are allowed to be in control. Indeed, rather than being evil, their existence is necessary for us to live. However, in the majority of cases, these forces have taken the driving seat in the human spirit, thus causing all sorts of havoc. The only way to set this state of affairs right according to Sumohadiwidjojo is through active worship and surrender to God. To this end he created a practice called the 'latihan' (literally 'exercise' in Indonesian), which allows each person to surrender his will to the universal life force and to invite physical and spiritual movements of purification.

Here is the quote, from one of his talks (in 1967):

"If you want to know how demons manifest in their exposed state, look outside you, in the world. Here are the demons, right here in your glittering clothes. Money has demons in it. There are demons in your shiny shoes and demons own this beautiful building. How can you put them aside, how can you avoid them, since you need them while you are living in this world? Therefore do not be afraid of demons or hate them, because you need them. If they avoid you and are not close to you, you will not find your fortune nor make money. So you need to be close to demons, because what is most important for you is to be able to use them. When you are looking for money you need to take them with you and have them close to you. When you worship God you put them aside. When you worship God, there is nothing but Almighty God.

Therefore do not be afraid of demons or hate them, for they are your servants. If you are not supported by the satanic, by the vegetable forces - by plants - and by animal forces, you cannot live in this world. That is confirmed in medical science. If you do not have the disease within you, that is when you can catch the disease. If you have it within you, you will not get it. That is why you are inoculated against the disease. You will not catch smallpox if you already have it within your body. You are inoculated against smallpox so that you should not catch it. When something is absent, there is a lack of balance, with the result that you are very easily affected. In the same way, if there are no demons within you, you will be in trouble: you cannot survive, you cannot earn a living and you cannot make money. So you need demons, but you must be able to manage them."

I think what he has to say about inoculation as a metaphor is very interesting with regard to the article above.