The desire for realisation of Truth, for Liberation, or for God, is also a desire, which will cause some agitation, until it is fulfilled.
Desire by its very nature is such that it causes agitation and restlessness the moment it arises. While engaged in reading, writing or listening to something suddenly, a thought appears. It could be something as simple as, "I think I need a coffee break now." Immediately, the mind is disturbed and restless. If the desire for coffee is obstructed, and someone prevents its fulfilment, the desire turns into irritation and ultimately, anger.
One of the characteristics of desire, is that once fulfilled, it becomes greed. I just want a little more...then some more…and then even more…! It never stops. Throughout life this craving continues. Desires can be compared to a box of paper tissues. Like tissues, as soon as one is pulled out, another pops up; as soon as you satisfy one desire, the second is waiting for you. Fulfil it and behold — a third one surfaces!
To live, we have natural, physical needs - when we are hungry, we want food; when we are thirsty; we have to drink something. These are natural needs; they cannot be categorised under desire or kama. Consequently, it is necessary to distinguish between need and desire.
The desire for realisation of Truth, for Liberation, or for God, is also a desire, which will cause some agitation, until it is fulfilled. The significant difference being, that the desire for one's own upliftment will not force one to engage in sinful acts. Hence, it cannot be labelled as insatiable or sinful.
The desire that should be considered an enemy is the desire for more sensual pleasures, indulgence and gratification of the senses. Greed for more power, wealth and pleasures can never be fulfilled, because these desires concern the extrovert mind and the consequent seeking of pleasure in sense objects. They only multiply. Undoubtedly this category of desires are inimical to us and are very different from those that fulfil our natural needs.
It is a fact that some desires are strong and difficult to overcome. They cause so much pain that we want to give them up. For example, an alcohol or drug addict suffers and says, "I really want to quit." Unfortunately, even though, they truly want to be free, by then the habit is so ingrained, the inclination (vasana) so strong and deep-rooted that it cannot be easily overcome.
Another reason for "feebly" wanting to give up something is because we like it and do not actually want to give it up. It gratifies our senses and even though we know it is harmful, we secretly enjoy it. If we do not want to perform a certain act, nobody can force us to do it.
Desire is the enemy within that propels a person toward wrongdoing.