I keep seeing this post about Ace and his actions going around, and I also have some thoughts; however, the post is getting long, and my thoughts have taken a bit of a left turn. Mostly, because I think my interpretation of Ace might differ from a lot of those in the post and therefore lends a different rationalization to his actions. So this post is mostly my interpretation of him.
I think the closest of those who post who share my interpretation is @sentimental-mercenary. They say:
I’d like to also point out that fighting in an army does not mean 100000000% supporting the ideology of that army. A little research into the ‘comitatus’ would probably do some good here–military units coalesce around a homosocial code, so you tend to fight for your guys, rather than for that abstract idea. In other words, when I was in a firefight, I wasn’t like YO BALD EAGLES FREEEEDDDDDOOOM, or even YAY PRESIDENT, I was like, SHIT they’ve got Smitty pinned down. When someone betrays you in that system, FUCK YEAH you take it personally.
I think this sums out very well how I see Ace, because Ace is old. Ace is quite obviously between Joe and Max's ages. He didn't grow up in Citadel. He comes from a different culture and has adapted to War Boy society.
I interpret Ace as knowing better, understanding that he is living in a post-apocalyptic society of oppression and toxicity. But he's survived this long, which inclines me to believe that he hasn't so much as fought the system but rather found meaning within it.
I believe Ace bows his head reverently at Morsov's death for Morsov, and for all the other War Boys who will live better knowing their deaths will truly be honored by someone who matters to them.
I believe Ace bows his head reverently to Joe to show his subservience. To prove that he believes in this world, even if he doesn't, so Joe let's him keep his post.
Maybe he falls for it a bit, but I think he only does so insofar that he knows it's the meaning the War Boys have found.
When you live close to death (which most people who can fart around on Tumblr probably don’t) you DESPERATELY want meaning. You desperately want to believe that there’s some sense or logic–if not in a sort of ‘magical thinking’ ritual you follow, then at least in the sense that when you do lose your buddies, you want to believe that it was…for something, or that they went some place other than a plastic bag. Because if you can’t…it crushes you. —sentimental-mercenary
Ace probably came to believe that yeah, this was the best we could have of a society in this seeming end-of-times, so the deaths on missions to keep it turning are helping humanity hold on, but I also think it's far simpler than that and that he just wants to make sure that they don't live their lives in despair and know that even if their lives and deaths are meaningless, they won't be broken by the despair of ever knowing that.
I think Ace found meaning in helping and protecting his War Boys. He knows he can't protect them from battle and illness and death, but he can protect them from a meaningless, useless life. He has no power to do anything else, so this is the path he's chosen to take. And Furiosa was a leader who appreciated people for their individual abilities and that translated well into caring for his War Boys. I tend to also hold the headcanon that Furiosa didn't ask for needless, dramatic deaths at the drop of a hat. She wanted a working crew to get the jobs done, which means she valued her men, and Ace values her for it. He respects and appreciates her for it. He probably finds a bit of a kindred soul in it perhaps.
So when Furiosa does the unexpected, he doesn't immediately think she's putting the crew at risk. There is something to be said of 'following orders.' It is certainly possible she had been given secret orders, and the War Boys, who are literal canon fodder, to be expected to follow along obediently. It bothers him that she didn't trust him with the task, but perhaps he even reads in her hesitations that she wishes she could.
But when she's driving the rig at a giant sandstorm with no protection for the War Boys on it, he's upset. He realizes he's been betrayed personally, because he had dedicated the rest of his miserable life to bring meaning to the War Boys under him, and she was driving them to a useless, meaningless death as he saw it.
So I do think he's angry, desperate. And I do think he wanted answers from her. I don't think he would have been entirely against escaping from Citadel. He doesn't know when he first suspects it, if he's alright with it. He'd like to give his boys a better life, but what of those left behind? Maybe he had even had some hope himself, to be a part of an escape plan, to take himself and these boys somewhere far away from that toxic place. But then he realizes that wherever it is she's going, for whatever purpose, she has decided that he and his boys don't have a place there. They are, once again, canon fodder, and yes, he feels betrayed.
I'm sure one can imagine why I might harbor some sympathy for ‘Good Guy Ace.’ In the face of feeling powerless to fight against the oppression of the society, he carved out for himself some meaning, that being of bringing some amount of kindness and compassion into the lives of these boys who are taught nothing but war and competition. I appreciate that he thought he found a like soul in Furiosa, and my interpretation that even she had in fact found some life and meaning with this very crew.
But it doesn't make him less complicit, and it doesn't make it any less necessary for Furiosa to leave him behind.