Just read your prongsfoot analysis in response to anon. I agree with what you said, except the bit about Sirius’ admiration for James. It was definitely not a coincidence that James was a pure blood from a respectable line, but I don’t think that’s why Sirius let himself admire him. I think that yes it’s the privilege that gave James more freedom to develop the traits Sirius was drawn to (the confidence, the mischief, the bravery and sense of justice etc), but I do believe that Sirius would’ve been just as capable of admiring and even marrying someone who’s not pure blood. I do think he’d deconstructed a great lot of the blood purity rhetoric. The hang up is that he definitely thought he and James were better than everyone else but based on his metric of skill. Even if he were to date a woman, I think she’d have to be fiery but I struggle to see him carrying if she’s muggleborn nor not.
I loved everything else you said and this is more of a what came first question that I’m raising
For that to happen, he would have had to deconstruct himself, and in order to deconstruct himself, he would have had to acknowledge that he was wrong and Sirius never admits, nor even considers, that he might have been. Even when Harry confronts him about what happened with Severus, it's Remus who genuinely comes across as KNOWING that what they did was wrong. Even if he excuses his friends, Remus is still aware of where the problem lay. Sirius isn't. Sirius just keeps pushing and pushing and being an asshole. He has absolutely zero self-awareness and is even incapable of seeing why, regardless of whatever Kreacher might say, treating him like shit from a position of power is deeply problematic.
At no point does Sirius truly question his own privilege because, from his perspective, being blasted off the family tree was already some monumental act of rebellion. He has no class consciousness whatsoever and is incapable of viewing things through the lens of someone genuinely educated in social issues. Sirius sees James as an equal, and outside of James, the only people he regards as equals are directly connected to James and function as extensions of him (namely Lily and Harry). Everyone else, he does not see as an equal, and it shows in the way he treats them.
He doesn't even consider Molly Weasley his equal, and I'm saying this as the number one Molly hater here since she's one of the characters I dislike the most. But Molly is absolutely right when she confronts him, and he reacts like a sulking child throwing a tantrum. He uses Remus for his entire life: first as a source of entertainment, then as the only friend he has left alive because he has no other option. He never respects Severus, even when he knows Severus has shown more courage than Sirius himself has ever demonstrated in anything. And what's the common denominator among all of them? In one way or another, they are all socially or economically beneath him.
Classism isn't usually conscious. It's something we absorb structurally from childhood. In British society specifically, it is especially pronounced, and among aristocratic elites, it's practically in the blood. You cannot understand this from the perspective of someone born in a country where caste systems don't culturally exist or where status is determined merely by financial position. It has to be understood through the lens of a class society built upon a traditional aristocratic system.
Sirius respects James, and that makes sense because James fulfils two conditions: he is socially and economically equal to him. Socially, because of blood status; economically, because his family is wealthy (he could have been impoverished aristocracy like the Weasleys, but that isn't the case). Ignoring this aspect means ignoring how class systems function, and it also reflects a significant ignorance regarding how people are raised within aristocratic elites. I come from a society that still has a monarchy today, and therefore retains aristocratic structures. There is an enormous difference between the bourgeois perception of status and the aristocratic one. And the worldview in Harry Potter is aristocratic because that's the environment its author comes from, and the world she created is based on that kind of society, whether people like it or not.
You have a very naïve and childish understanding of how people work. I've met people from extremely powerful families —both golden children and black sheep— who have spent YEARS in actively left-wing political circles and have read countless books on how not to become as classist as Mum and Dad, and yet they always, always display behaviours that stem from what they absorbed at home, to a greater or lesser extent. And, coincidentally, they ALWAYS end up with partners who, even if they don't come from elite families themselves, at the very least come from families with well-positioned parents and have lived comfortable lives.
And yes, that person may look like they crawled out of a landfill because they dress as though they haven't showered in three weeks, but they still come from extremely comfortable backgrounds. Cinderella is a lovely story, but everyone conveniently forgets that before her stepmother stripped her of her wealth, Cinderella was the daughter of a minor nobleman. In other words: the prince didn't marry a nobody, he married someone who was entitled to a title herself. Disney doesn't tell you that part.
Sirius wasn't deconstructed at all. Repeating like a parrot that blood purity is wrong is one thing; practising what you preach is another entirely. Sirius treated people beneath him socially and/or economically with immense condescension and arrogance. He didn't respect them. He didn't respect Remus, he didn't respect Peter, he didn't respect Severus, he didn't respect Molly (who was socially his equal, but not economically), and the only people for whom he demonstrates genuine respect are those directly connected to James.
That isn't deconstruction. That's rebelling against Mum and Dad's ideology, recognising that their ideas are bad, and then believing you're a hero because you ran away from home. Spoiler: if you treat your house-elf badly —a being who is literally your property because you haven't even questioned the morality of being a slave owner— and your excuse is that he was loyal to your mother, then you are not deconstructed. Because if you genuinely cannot see that you are HIS OPPRESSOR because you are HIS OWNER, then you are not deconstructed.
Sirius was NOT deconstructed.
That doesn't mean he didn't have good intentions, nor that he didn't fight on the right side. But spoiler: your most feminist male friend can still be a rapist. Spoiler: your most left-wing friend can still treat waiters like shit. Spoiler: having a political ideology does not make you a better person, nor does it make you a good person. Applying those principles in your day-to-day life does, and Sirius didn't do that.
So, sorry, but I fundamentally disagree with the idea that Sirius was some hyper-deconstructed, highly self-aware individual. And I disagree even more strongly with the idea that, if Sirius had only been attracted to women, he would have ended up with a muggle-born daughter of muggles. At most, he would have ended up with a slightly progressive version of his mother. Because, among other things, the man had monumental mommy issues. But that's another story.
And I'll tell you something else: the brilliance of Sirius as a character lies precisely in the cognitive dissonance between who he believes himself to be (a rebellious, radically deconstructed hero) and who he actually is (a child with severe mommy issues who made the right choices but executed them terribly). Remove that cognitive dissonance, and the character becomes boring and clichéd.
Let Sirius Black be a grey character. Let him have his darkness. That's what makes him interesting.