This is largely a vote on how we present ourselves to the Imperium. That presentation will have a massive run-on effect on later things, but this is not a direct vote for those things.
We can present ourselves as willing to work within the structures of the Imperium, which is to say, the intellectual and cultural fabric of the entirety of the rest of our species, representing thousands of years of literature and poetry, culture, and theology, a shared idiom making us intelligible to our fellow humans. Or we can essentially kick all of that to the curb and declare that we, uniquely, have all the answers. For outside observers, which one looks like we want to change things, and which one looks like a really charismatic daemon prince has managed to infiltrate a Shrine World? That's happened before. More than once. The well has been thoroughly poisoned here; one of Chaos' most potent and insidious weapons in stymieing positive attempts at reform.
Ultimately ctulhuslp is wrong, vastly underestimating the scale of the problem here. We cannot both hope to save humanity, and not present unavoidably a threat that the Imperium will feel forced to either work with, or wage unrelenting war against militarily. We cannot just quietly sit in our single sector improving our granary management stats, and slowly levelling up our skills. We cannot just be the Tau, carefully and slowly expanding a compact territory. Or we could, but to do so is essentially to give up on our reason for existing. Humanity is dying right now. It will take a massive preponderance of military might to even hope to save it. We are going to need to expand our powerbase dramatically and keep doing so, grabbing every iota of strength we can. That is not something the Imperium will just stand by and ignore, they cannot ignore it; we will look like another incipient Horus. That is before one considers the literally apocalyptic implications of our heritage and our personal claim to the Throne.
We can either take over the Imperium, and take the Throne, after sweeping through on a wave of religious reawakening and miracles, perfectly playing our hand to convince the people and leaders of Humanity that we are their saviour, before finally revealing our parentage. Or we can declare war on the Imperium and watch is it burns to the ground, and its people burn with it, hoping to rebuild something better from the ashes. But we must do one of them, because to have the power we need to do anything of importance, we cannot simply sit around twiddling our thumbs trying to quietly level stats. This vote right now does not totally lock in either of those options, but Defiance makes outright conflict more likely. Not certain, but inarguably more likely.
As for what Imrix says, I understand where he is coming from but I think he confuses the possible with the actual. It is true that there are any number of alternate systems that, in the abstract, would do the job of the Imperium much better. It has any number of terrible, almost tragicomic negative externalises and problems; this is baked into the setting. But right now, at the dying of the light, where we find ourselves, it is the only structure able to provide a collective defence for most of humanity. If the Imperial Navy and Imperial Guard do not wage pre-emptive wars against the enemies of humanity, breaking up Hive Fleets and Waaaaaghs! before they arrive into populated sub-sectors, forcing the bulk of the fighting into buffer zones via proactive defence, then the majority of humanity are going to die, and die horribly. The fact that it is a supremely imperfect at doing so does not change the inconvenient truth that it is the only thing doing so. The one thing the Imperium reliably delivers on, as dysfunctional as it is, is collectivising humanity's resources on a massive scale and using them to wage war. This too, is baked into the setting. We, just logistically right now, will simply not be capable of reaching the vast majority of human space before it falls to invasion when a weakened Imperial Navy finally folds. At best we will be able to avenge them, and reconquer what is left.
As I said above, I can actually respect the argument that maybe pragmatically, that is the only thing we can do, and trying to save most of humanity is just not practicable. Notably, this is the same judgement the Emperor himself made, when he waited to launch the Great Crusade, building his forces in Sol, leaving humanity to the terrors of the Age of Strife.
But I don't want us to repeat the sins of our Father.
