I would not describe the sacrifices made by guardsmen, manufactorum labourer's or really any of the low grade meat that gets ground up in the Imperial war machine as nobly sacrificing. They lack the capacity to sacrifice themselves, the decision was made for them and they live in cultivated ignorance so the people who are making that sacrifice can keep them cowed.
Does that make their deaths less worthy? Does that make the cause not worth fighting for?
If the average guardsmen knew what an ork was like rather than the propoganda that tells him they're even more pitiful than gretchin the amount of bolt shells it would take to keep a regiment of drafted cannon fodder in line would be astronomical.
Ironically enough, average Guardsman probably knows, mainly because the ones that don't know die very fast, and the veterans make sure the fresh recruits realize what they're against. There's a reason why Imperial Guardsman Uplifting Primer is considered to be toilet-paper level stuff even in-universe.
If the average citizen knew that Chaos existed then the amount of cultists on any given world would increase drastically.
Possibly, although the average citizen isin't in such bad position, and while it's not up to me to question the Emperor's choice of witholding such information from humanity at large, populations which realize what Chaos truly is usually tend to fare better off, since they actually know that it's bad idea to deal with it.
Indeed such is common, few mortal men can actually stand against the horrors of the galaxy, most die gibbering and mad, trying to cram organs back into broken bodies or bleeding from the eyes as their minds erode before unamed terrors.
And yet they do. The mere mortal men stand against the horrors of Galaxy, despite being the same as men who die gibbering and mad, trying to cram organs back into broken bodies, or bleeding from the eyes as their minds erode before unnamed terrors.
The normal citizenry are cattle, cowed and branded and fed into the slaughterhouse to preserve order and peace on scales no normal mind can comprehend. In the Imperium someone has sat down and reduced every conscript, every hive labourer and every child into numbers and statistics and worked out who is worth sacrificing. The sacrifice made by the ordinary is not a conscious choice, it is a decision made by the Inquisition, the Administratum, the Mechanicus and the other forces that govern the lives of mortal men. It is no coincidence that these groups are all more inhuman as you rise through the ranks, nor is it coincidence that the Astartes are inhuman.
But who are the Inquisitors? Who are the Administratum? Who are Mechanicus even? Are they some heavenly forces that cannot be percieved? No. They are human. Every single one of them.
The Inquisitors are the ultimate individual, they think freely and they do as please, with their every action bordering heresy, because sometimes the only way is to fight fire with fire, and only the strongest amonst us can stare in the abbys and not fall.
The claim that Administratum is inhuman is laughable, for they are probably the most regular grey folks as there can be. In a way, they also sacrifice their lives to uncountable counting for uncountable decades, just so that Imperium doesn't collapse and every food shipment finds it's place.
Mechanicus become inhuman due to purely human reasons. Their Quest of Knowledge is one of most human undertakings in whole Imperium. They sacrifice parts of their own humanity on the altar to machines, just so that humanity might be triumphant one day.
Astrates aren't inhuman. They are
more than human. They have passions, hatreds, feuds and live on larger scale than mortal men. Where they walk, earth shakes. They are god-touched, like false deities from an old opera, they boom and thunder. Every emotion is magnified, every weakness spreads into a catastrophe, every strength is almost overbearing. They can be poets and tacticans and great leaders of men, but they must fight if Imperium is to survive. They are inhuman in that way they are beyond humanity, they are the ultimate we should struggle to be.
In the 41st millenium the true tragedy isn't the lives of soldiers lost in war, it's not the mangled bodies broken by munitions factories, it's not the lobotomised servitors shuffling after uncaring masters, it's not the innocent burning alongside the guilty. It's the loss of humanity in everyone involved. The reduction of men into meat and numbers, the callous indifference it takes to reduce them to that level, the stunted personalities and broken minds of Skitarii and Space Marines, the cold and blackened hearts that are able to kill an entire world to save another rather than fight to the last to try and save both. It is that humanities defenders and those that forge their weapons and shape their armour had to abandon the very thing they protect, their humanity, and that the choice to do so wasn't even theirs to begin with.
It is easy to disregard everyone in the Imperium, think they're just mere numbers... after all, "A single death is a tragedy; a million deaths is a statistic..." but every one of those million deaths is also a single one. Behind every damn number, number of men, soldiers, number of deaths, servitors, number of births, lies a human life. A human life that adds up to a beautiful choir of life, of human life. It is a tragedy, but it's also beautiful, because on first glance what you state is painfully obvious. Everything is broken, humanity abandoned... but if you look closer, you will notice it. Every Guardsman had his family which he hopes is safe. Every factory worker comes back to his wife and children every day, after long, long hours of work. Every basically enslaved crewmember of the giantic cathedral ships cruising through the abbys of space dreams of his homeworld. Every Inquisitor carries the weight of the sentences he issued. Every Space Marine fights arm to arm with his brothers. Every Techpriest values his knowledge and hopes that whatever he discovers will make things better. Every Korpsman cries when it's raining. The list goes on.
The Imperium might lack humanity, because it's an organization that is the sad result of every bad decision and screwup combined. But Imperium in it's core is human, because it's humans who make it up, and they haven't lost their humanity. Not yet.
Also, after all... did you have any choice? Have you really chose to be born in the family you were born in? Did any of the conscripted soldiers in many wars choose to take part in it?
Does that make them less human?