Here is what I understood of the whole story :
In the beginning, only the Eternals existed. The Eternal King at their head, the Seven Lords/soon Gods under him.
Fane discovered the Veil between Reality and the Void, a dome of pure Source, some sort of cosmic energy.
The Eternal King said to Fane "DON'T YOU DARE STUDY IT MORE OR BAD THINGS WILL HAPPEN"
Fane said "fuck off" and went to inform the Lords about his research.
The Lords are greedy bitches (all seven of them... wow, that's bad luck for the King), so they drained the Veil and confronted the King, poor guy was casted out into Oblivion.
A war ragged between the pro King and the pro Lords (I guess the pro Lords were... only the Seven Lords themselves lol), but because they had Source as a weapon, they destroyed/sent a lot of the Eternals into the Void with the King.
For whatever reason, they all survived : the most powerful of them all, the King, became the God-King, some kind of Void God, the rest was transformed into Voidwoken (Fane say to us at the beginning "Eternals were from many shapes and sizes", and we can see it very well with the many Voidwoken species). But they ALL became corrupted by the Void, the God-King being the most resilient, he's still able to speak and stuff. The God-King wants to come back as the ultimate ruler of the world, and yes he's the victim... but now he's a mad and corrupted ruler who wants to enslave every mortal
Back into the present : the Seven Gods are awful beings, they created the mortal races (mortal for a good reason) to feed upon their soul/source (really similar) --> it's like if you use a bit of your power (Source) to create more food (mortals), and later you will feed upon this greater source of power (your original source imput x 1 billion of dead humans for exemple). The Hall of Echoes is basically a fast food for the Gods.
But because they drained the Veil, the world of the bitchy Gods is under the pressure of the Void, and that's why they all give a bit of their power to a Divine, their ultimate agent who must protect everyone against the Void while the Gods do nothing and feed upon the mortals.
But ONE DAY, Lucian the Divine was so badass that he discovered by himself that the Gods are evil (after all, they drained the power of the creation for themselves even if it meant the end of everything because of the Void, aaaand they provoked the extinction of their race). His plan is "simple" and... how do I put it... oh yeah, CRAZY : with Dallis, he wants to GENOCIDE EVERY PERSON WITH SOURCE IN IT. Every living person ? I guess not, so more like every person with a lot of Source in him (Sourcerers and Godwoken). Then, he will use the Source of everyone to repair the Veil, ending the Void threat.
And here is the main plothole : EVERYONE HAS SOURCE. PEOPLE WERE CREATED TO SERVE AS SOURCE FOOD FOR THE GODS. So if Lucian needs ALL the Source, nobody will be left alive ??
In the end, I guess Lucian meant "I need all the Source possible, from the Gods first, then Sourcerers THEN Godwoken, normal people are nothing". But I'm pretty sure the Source of millions of people is still a big deal in a plan to harvest nearly all the Source...
Problems : if mortals still exist, so too the Gods, so they will ALWAYS drain people in the Hall of Echoes. And they will also always drain the Veil... so Voidwoken will come back anyway. Nice plan Lucian.
And OP, you don't understand why "eating the soul of a person, destroying it forever" is evil ? Really ?
The universe of the game has an after life ! Eating a soul is like in our irl world : void/oblivion/non existence/nothingness.
It's like if in the real world, someone said "hey, after life exists, it's a really nice place where you can sleep/live with your dead family, for as long as your want... BUT the Gods will eat you one day". That's not nice.
