Unmade Origins
Most people probably already know this but Unmade are named after deities of the ancient near east, they also have some linguistic connections to Urdu/Hindi languages:
While this might not hold any significance i believe this isn't a mere coincidence, they are ancient godspren.
I find this quote particularly interesting, it depicts Unmade as related to human emotions, not people, not parshmen. This connection might suggest that Unmade share their origin with humanity - the devastated world of Ashyn. Just as Stormfather embodies Highstorm or Nightwatcher - Transformation, Unmade would personify forces which shaped the world itself - powerful emotions that defined life on Ashyn. At first, i considered each one to represent particular Vice, like Wrath or Gluttony, but there's much more to them:
They are not inherently good or evil, they are both, Vices and Virtues depending on one's perception. Each Unmade embodies the whole spectrum of a particular passion, just like Nergaoul personifies will to fight, some could interpret it as desire to protect, others to conquer.
Divine Attributes
We all know that each Order has set of Divine Attributes linked with it, apparently, they are somehow connected to the Unmade. I assume every Radiant has innate Virtue/Vice, related to Divine Attributes.
A secondary surge of each order is considered dangerous. This is something that is mentioned over and over, Jasnah warns Shallan about Transformation, Nale says roughly the same thing to Szeth about Division, etc. Obviously, it's not relevant to the nature of power itself, because adjacent order gets it as their primary surge.
Philosophically virtue is an elusive concept, it demands careful and sustained reflection before it can become part of one's life. Radiants seem to share this view, giving the nature of their Oaths. Pursuing a Virtue blindly and failing to understand it, might turn it into a Vice. Perhaps danger associated with the second surge, is related to twisting an ideal into something bad, possibly exposing Radiant to an Unmade/Odium?
Virtue lies in Divine Attribute linked with corresponding Order. For example, Windrunners exhibit will to Protect people and show great capabilities in Leading them. Their attitude/perception makes the concepts of Leading/Protecting easy to grasp and comes naturally to them. Vice, on the other hand, is related to Attributes of adjacent Order.
Windrunners or at least Kaladin, struggle with the idea of Justice. Kal view of this ideal is distorted, he takes it personally and allows emotions to cloud his judgment, his attempt at being righteous almost killed Syl. On a side note, Jezrien translates to "the Judge" in urdu, coincidence? While Moash still shows the attitude of a Windrunner through his desire to protect Parshmen, he contorted Just into Vengeful and led him to Odium.
Similarly, Szeth stumblings revolve around being blindly obedient and not brave enough to challenge his masters. He mustered the courage to defy Nale and escaped Odium grasp as opposite to the rest of Skybreakers.
If my assumptions are correct there is no Unmade related to Pious/Guiding attributes. I hate to poke a hole in Talenel's immaculate image but he remained unbroken simply because there is no Unmade corresponding to his Vice, not his unbreakable will. This gives at least some semblance to Heralds idea that he could handle tortures indefinitely, i assume they would need more substantial argument than just Taln being stubborn and blessed with strong willpower. Keep in mind that this not means being immune to influence of the other Unmade.
Another piece giving this reinforcing this theory is particular relation of Thrill, Dalinar and Kaladin.
Kaladin might not feel the same Thrill as other men do but still, have similar exultation. Stormlight drives him to action, grants immense focus and endurance, in the same way, as Thrill affects Dalinar. I suspect Windrunners share this characteristic, they receive purified version of the Thrill devoid of bloodlust. While this feeling is empowered by Stormlight/Honor, Kaladin felt this before bonding Sylphrena, thus this seems more like a natural affinity.
Conversely, Dalinar is super susceptible to this effect, to him violence is intoxicating and addicting, he revels in conquest. Perhaps this is the reason why Bondsmiths bear no Blades, as a reminder of their Vice. Apparently, this correlation encompasses each pair of Radiant Orders and Heralds, one's Virtue becomes Vice of the other.
If proven true, this theory could provide an answer to most persisting questions, the madness of Heralds, a reason for Recreance and Cataclysm of Ashyn. Let me know what you think.