The moral of the Vox revolution? "If you want to change the world, don't lose your humanity in the process."
Like the various real-life revolutions mentioned in this thread, that's what happened here: The Vox went from being oppressed to exterminating every man, woman and child of European descent. They went from suffering great evil, to committing great evil. The game set up our hopes things would turn out for the better; it made us sympathetic to the Vox and why they felt the way they did. But it also showed us the real-world peril of revolution, the risk of fighting monsters and becoming one in the process. In this case, the Vox became their own sort of racist, and one where the utter destruction of anyone not like themselves was the only way.
Violence begets violence. But will the circle go unbroken?
Also, as EliCash said, it's good they didn't whitewash Daisy. The "PC" route would've been to make the black revolutionary a saint, but that would've been boring and disingenuous. In the end, she showed her own corruptibility to power. One of her recordings even indicated the "white man has no place at their table" or some such. Reminds me of another videogame depiction that tried something similar, namely the Mexican usurper in the second act of Red Dead Redemption. You help him displace the dictator, and then as you're heading out of Mexico, you can't help but wonder if they're really better off than they were before, even though the new dictator was the "voice of the people" (the English translation of Vox Populi, btw).
In my view, the handling of Daisy's character and the Vox in general was very much a copout by a writer who was afraid to make a stand one way or the other on the various issues and politics (simplistic as they might be--which in Infinite's case is extremely so) brought up in the story, and so took the easy way out and sat on the fence, painting both sides as no better than the other. On the other hand, that's not to say Daisy should have been portrayed as a 'saint', but with the way the whole story went down I was left wondering what the point of her inclusion was if anything other than filler to pad out the game. It would have taken more balls to portray one triumphing over the other through a great script, than simply washing hands of Daisy and the Vox.
And this notion of the rebel who becomes that which he fought against is also very much a cliché. Nothing new there.
At least in RDR the similar scenario was handled with a bit more subtlety, and had more facets to it in terms of characterisation and story arc than the rather simplistic and throwaway approach in Infinite.