When humanity finally united and ventured into space, our ideals became: individualism, love for others, and spirituality. We sought the divine, while respecting the rights and freedoms of all living beings, regardless of their race. We hoped that the Galaxy would respond in kind.

Xenophile, Egocentrist, Spiritualist.
We were wrong. The very first contact with aliens showed how naive our notions were. While ordinary people rejoiced at the discovery that we were not the only intelligent beings in the Universe, politicians expected war. And how could they not, if the only thing said during first contact was "all humans will be destroyed."? And although we tried to prepare for war, we turned out to be completely unready for it. When the aliens attacked us, their demands were absolute — surrender all planets belonging to humans so that humanity could be completely exterminated in the future.
During a protracted war, during which the colony at Alpha Centauri changed hands several times (fortunately, they did not have time to carry out their plans regarding the population), after long preparation of the fleet, a decision was made to engage in a general battle. That very colony was chosen as the location. The enemy fleet was lured into a clever trap, and while it tried to destroy a quickly erected military station, the human fleet attacked them from the rear. Nevertheless, the aliens were numerous and fought with incredible ferocity. Despite a significant tactical advantage, many young boys and girls gave their lives that day. And although the price was terrible, humanity was saved — the xenos abandoned their demands and agreed to conclude an armistice.
After the war ended, it was first decided to restore destroyed space stations and homes and focus on returning to normal life, as it was expected that the opponent would do the same. But intelligence reported with horror — the aliens didn't care about restoring peaceful life; they were already preparing a new fleet. Since it became obvious that the xenos simply would not stop until they finished off humanity, a decision was made to also postpone infrastructure restoration and focus on creating a fleet. Once the fleet was deemed ready for attack, a preemptive strike was launched with a demand to fully transfer all planets to humanity — unfortunately, after seeing such bloodthirstiness, it was decided that this race could not remain independent. Nevertheless, after victory over them, they were fully integrated into human civilization with full citizenship rights.

These guys. By the way, I got really lucky with mushrooms; almost the entire galaxy consisted of nothing but mushrooms.
The first clash with the unknown did not frighten us. It didn't make us more cautious or paranoid, nor did it turn us into closed-off sectarians. We understood that this was merely a trifle on our great path. And we boldly took step after step forward, into the unknown. We wanted to find the truth, which essentially meant finding the divine. For it was clear from the start that the Universe could not exist without a divine beginning. Therefore, when it became clear that we had finally found it, we did not slow our pace. And we stepped straight into the Abyss, ready to pay any price.
The first thing required of us was our human appearance. Perhaps our rulers would have been cowards, wouldn't have taken this step and thereby stopped this mad path to destruction. But the first steps were taken by them unconsciously, by mistake, and when it finally became clear where everything was heading, it was already too late to turn away from this "gift".

Before and after.
After that, many terrible and inexplicable things happened, but they always required human sacrifices. Therefore, when we had to extinguish the light of our star, our Sun, to receive the love of our deity, we weren't even surprised.

And it wasn't only the light of the Sun that we had to pay with. Everything living on Earth died. Absolutely everything. Except humans. Although could we still be called humans? The same fate befell Mars, where life had begun not so long ago through our efforts — only to be later destroyed by us. Truly, we reached a divine level — "God gave, God took away".
Of course, we did not go without reward:

And keep spending influence on buying new leaders...
But no matter what the gifts of these deities were — was this what we wanted at the beginning of our journey? Could we have thought that the pursuit of truth would lead us to a nightmare? But truth is truth, whatever it may be. And to comprehend it fully, to the very end, one last step remained for us. We gave ourselves to these gods, the population of our and some other planets; we gave them the light of our star and our souls.
But the rest of the Galaxy was still alive. And so we gave it to them as well.

And now tell me how you're getting wrecked by fallen/unbidden...
That's how it went. The second half of the post turned out overloaded with images, but what can be done; I expressed my thoughts as best as I could, and I also wanted to show the pictures. Interestingly, I was just thinking about starting a game by destroying vile xenos in the name of the Emperor, and throughout the game I could observe how the Gameplay leads me to this step, as the most logical and correct decision. When I turned humanity into monsters, I actually felt like Lorgar, as described in the book "The First Heretic". Oh, and just for a checkmark, I did take the victory.

Psionics have a bug — if you give the gift of psionics to a second/third/fourth race, it is considered the primary race. Fixed in patch 1.6
Where do we end up when we save the world?