A donkey, in Ibn Sīnā's example, possesses no less than three faculties for discernment, the simple, the vegetative, and the animal (spirited). These all contribute to his well-being by allowing him to discern different levels of Good; the vegetative faculty tells him that grass is tasty, but when a lion appears on the horizon, his spirited faculty tells him that continued life is better, and he accordingly runs away. He chooses the greater good over the lesser, and this is a sign of his acting according to God's plan, a behavior that is fundamentally good. Humanity is merely expected to do the same. Possessed of the capacity for discerning sublime truth, we should be able to override our appetites just as the donkey did and choose eternal pleasure in virtue over the temporary pleasure of earthly desire. It is not that the desire of the appetitive soul is inherently bad, it simply needs to be held in check by the higher faculties at the appropriate time. The bulk of humanity, of course, rarely strays beyond the appetitive faculty of other animals, and therein lies our shame; we dishonor our Creator by ignoring the capacity for exalted thought we possess.
I find it interesting that in this text, as well as some of the others we have read, Ibn Sīnā does not see any fundamental difference between humans and other animals as far as how our minds work. Like humans, animals are capable of discernment and choice between lesser and greater goods. The only thing that separates humanity from the rest of the animal world is this question of capacity, which is more rooted in the realm of the potential than in that of the actual.
You might want to check out:
Von Grunebaum, G. E., ‘Avicenna’s Risāla fī ʾl-ʿIšq and Courtly Love’, Journal of Near Eastern Studies, 11 October (1952):4, 233–238
Bell, Joseph Norment, ‘Avicenna’s Treatise on Love and the Nonphilosophical Muslim Tradition’, Der Islam, 63 (1986):1, 73–89