I just realized what a beautiful setup Maggard was and that he likely played a NOT insignificant part in converting Horus.
Here's a warrior, a GREAT warrior, but a baseline. How has the Imperium treated him? The HUMAN Imperium, the baseline culture?
Tongue cut out, life-bonded to an aristocrat that he will protect til his death. If he fails his life is forfeit. His voice has been taken; he has no value beyond the function of protection and weapon. He has no rights beyond that. Petronella all but explicitly rapes him, too. There is not a part of Maggard's life that isn't ruled by her. He, the warrior, belongs to the sedentary nobility. All that he is has no value to them. Beyond service, and utility. Petronella does not recognize his honor. Humanity does not. Horus watches this. It disgusts him.
To Imperials, this seems right. Maggard is a warrior so skilled that he, as a BASELINE, earns the respect of astartes and primarch. He has no honor and no place amongst Imperials. He sees no reward. He only frightens them and so they want him punished for it.
Horus sees how the Imperium will treat him here, too. How it might already BE treating him! No tongue, you have nothing to say. No life intended beyond your function. If you have no function you'll be killed; for Maggard that's explicit. For Horus,.. not yet. But he will soon realize. If he finishes this crusade and people like Petronella install themselves in power, he will become Maggard, his sons will become the same. If not so already. Astartes have no place there; they "shouldn't rule". They leave bureaucrats behind them to grow a system that won't fit them. They don't retire. The framework of the imperium is not set up to receive them. The framework of the imperium does not honor a warrior with reward. Not outside the crusade, where they are in their own culture. It only uses them. It will dehumanize them when the time comes to control them.
What would happen to Maggard if Petronella died? The same that would happen to Horus if the crusade ended. The same thing. Horus sees self determination stripped away, and loyalty unrewarded.
