Isn't an overwhelming desire for Vengeance against a crime commited thousands of years ago a Sin?

I don't know if this is what the devs actually thought or if it was an unusually elegant reading of the Sins story by an early forum user, but my favorite explanation of the Sins races is that each represents some of the main evils of the 21st century.

1. The TEC represent the evils of unrestrained capitalism, populist democracy and consumerism. The TEC have no respect for the natural beauties of the universe, to them exploring and finding new worlds is only a means to make more profit. The exiling of the Advent shows an intolerance to a cultural minority, and the TEC Rebels takes this to a whole new level with paranoid xenophobia. While individuals exist in Trader society, it seems these humans only desire is to selfishly increase their material well being.

2. The Advent represent the evils of all consuming revenge, religious extremism and collectivism. While the Advent's exile may have been unjust, they have turned their anger over this into an unfulfillable desire for revenge, even though the original perpetrators of have long since died. This desire for revenge plays a central role in their religion, and ensures that their is no place in Advent society for infidels. The Advent seek to bring their unity to all of the sentient beings of the Galaxy, and any that do not convert will be mercilessly extinguished. Questioning of religious doctrine appears to be totally off limits, given the bloody split between the Loyalist and Rebel factions.

Finally, while individuals appear to have some agency, there is no privacy in the unity, and each of the unity's members merely exists to serve the whole. The Reincarnation ability on the Progenitor mothership suggests that lower ranking members are expected to perish so that veterans can return in their bodies, while the scout frigate shows that the Advent will gladly sacrifice themselves for their cause.

3. The Vasari represent the evils of Authoritarianism and Slavery. The former is pretty easy to understand; the old Vasari Empire ruled over countless sentient species and forced them to do their bidding or be annihilated from orbit. The enslaved labor tech suggest any Trader or Advent prisoners do little better. However, even for the Vasari themselves, life is likely not that great. All political power is concentrated at the top, and their is no evidence there is any room for dissent among the ranks. The masses are controlled with an endless stream of propaganda, and all aspects of Vasari culture now appear to be centered around supporting the military and the migration. The Vasari also seem to think themselves inherently superior to the human races, given the glory of their old Empire far surpassed the Advent and TEC and how easily they defeated the Traders in the beginning.

The point is for us, the modern audience, to see their Sins, and perhaps to reflect on how they manifest themselves in our world. What they think of their societies is irrelevant (and in fact without any real named characters in Sins it very hard to tell what any individuals think). And even if they do really like their societies (and I don't think you can assume that), that makes it all the more terrifying for us because they either do not realize their Sins or think it is proper behavior, much like how Nazis thought it was proper to cleanse minorities and for the Spanish inquisition to burn heretics.

*Cough* click here *cough* lol i wouldn't call my story a novel but check it out! 

That is actually specifically mentioned in the manual...

Whether a voluntary collectivist society is bad or not of course depends on one's political beliefs. But don't forget, they are also religious extremists. The Advent loyalists at least still believe that there is only one true spirit in the universe, the unity, and that everyone who is not apart of this community is an infidel. The infidels can either join the unity or they can die. Eventually all sentient beings will be brought into the collective community, as the rest will have been extinguished, and there would be no one left to question the one true faith. The fact their desert homeland was plundered and penetrated by overproud secular capitalists does not make them any more moral than the other factions.

And yes, I intentionally wrote that so that you could replace "the unity" with Islam and "The Advent" with Al-Qaeda and still largely make sense. The Advent are a perfect stand in for them. Their specific beliefs are totally different, as I imagine Al-Qaeda would be horrified with the idea of a society full of powerful, dominating women who are high all the time and limit men's ability to participate in important aspects of life. But their Sins are largely the same, mainly ideological intolerance, blind vengeance and an alarmingly excessive "us versus them" mentality.

I always knew you liked to be dominated Seleuceia. 

There is indeed an issue of punishment missing about Advent and a very unclear one about Vasari.

TEC sinned against a community that later become Advent and is now getting its face smashed for it. I wouldn't say that greed paid any important role here; for the most part, TEC was depicted as a prosperous and peaceful faction and it wasn't really greed that caused them any trouble. I mean, after thousands of years of peace, who in their right mind would've expected hordes of technologically superior aliens jump out of nowhere with lasers blazing... greed had nothing to do with them being unprepared.

Vasari... well, we can go on for hours about their "political" and "social" systems and why they are wrong, but we are not sure yet if that caused all the trouble they are facing. If it's a punishment, there is no clear answers as to what they are being punished for. Maybe it is some sort of nanite experiment gone wrong, in which case the sin is... what? Technological advancement? That would be pretty bold a statement, borderline medieval church doctrine that universally branded science as heresy.
Unless the "fourth race" turns out to be an enslaved race that was used as test subjects for some gruesome genetical experiment, the experiment went awry and the race was accidentally given imba psionic powers, which allowed them to bring down the oppressors and mount a vendetta... Unless that is the Ironclad's idea, I don't really think Vasari are being punished for being tyrannical douchebags. What are they punished for... we will have to wait and see.

And Advent is not being punished for anything. They developed their technology and twisted philosophy in peace (after being thrown out of their home) and are now running a successful crusade against TEC. That's that.