I don't know about greed, but self interest is the least disorderly instinct a creature can have. Your genetic line will die off very quickly if you constantly sacrifice yourself for society, which would mean the self sacrificing instinct would never propagate. Of course humans are social, cooperative, and self sacrificing under some circumstances, and that's good because we are often better off sacrificing occasionally. Maybe investing would be a better word. But some base level self interest is good. Kinda like how you're supposed to put your own oxygen mask on first in a plane emergency. If you try to get someone else's first, you'll both go unconscious and then you're both screwed.

the illnesses i'm thinking of are primarily narcissism and psychopathy.