We know (from Hamako) that there are only two kinds of Demondim spawn; the ur-Viles who loathe what they are and seek the power and knowledge to become what they are not, and the Waynhim who seek to give meaning to what they are by providing service to what they are not.
So I started thinking. Surely not every ur-Vile hates itself? Surely not every Waynhim chooses the path of peace and service? Surely not every ur-Vile serves Lord Foul? This lead me to ask how ur-Viles and Waynhim are created to be so different from each other.
We also know (from Hamako again) that the ur-Viles continue their breeding programmes in the catacombs beneath Mount Thunder, and that some of their creations are ur-Viles, some Waynhim. But why would the ur-Viles create more Waynhim? Especially since the Waynhim aren't considered the pinacle of the Demondim spawn. It just seems like a waste of time. Also, if the difference between ur-Vile and Waynhim is genetic, then wouldn't breeding programmes produce more strange hybrid creatures? Yet the only other Demondim spawn we see is Vain.
Perhaps, I thought, the ur-Viles simply produce a Demondim spawn, but have no control over which genetic variation they end up with. A kind of luck-of-the-draw thing.
Or perhaps, when each individual Demondim spawn is created, it looks at itself, realises that it "lacks the justification of birth", and then either loathes itself, or sees that despite the fact that it was made and not born it has the potential to give meaning to its existance through service, therefore deciding by its own choice whether it is ur-Vile or Waynhim.
So, what do y'all think?

Sum sui generis
Vs