As you say greed is part of the human condition - it's when it becomes obsessive that problems arise.
'Healthy greed' is no more than acquiring resources to live.(and why lefties have guilt about greed - (ie not understanding the human condition).
What could be more greedy than creating laws to 'legally' take resources off one person and then deciding who should get them?
Capitalism in it's truest philosophical sense - has nothing to do with money - it's the system that runs throughout nature. (we've just created the word in relation to money).
No money required.
All other 'economic systems' run against nature - top down social engineering that's not based on organic hierarchy (small social groups), but by entities not involved with a persons life, directly (governments for example).
The need for power for it's own sake does indeed lead to being 'Mentally ill'.
...Or they are nuts already, (more likely), and it's the expression of their nuttiness!
The Freudian perspective of super ego, id and ego seems to create a model that fits quite well in explaining behaviors (in my opinion, and though observation).
If it's anywhere near accurate - then 'the nuttiness' starts long before the acquiring of resources