Sure, people vary in their size, their physical strength, intelligence, education, wealth, etc. Another person's culture, language or appearance can be very different, and seem strange. They may do things you don't approve of. They may even have 'isms' of their own within that culture you'd like to see eliminated, such as women being oppressed. But to say that because of that, the members of that group/culture/etc are somehow 'inferior', and deserve a lesser status than you and/or the group/culture/etc that you belong to, is nonsensical.
I've somehow known all my life, long before I was able to put it into words (and I'm not sure I can totally do so even now), that every human being is essentially equal. Not exactly the same - we differ of course, as I said above. But beneath all that, is something, a spark, a common thread, a 'human-ness', whatever it is that forms the nucleus of our being. I tend to call it the human spirit or soul, but others will call it by other names. And we all have it, without exception. Even the ones thought 'unreachable', or 'too damaged', the ones who seem a threat, or 'too different to understand'. I've looked into the eyes of many considered 'other' or 'undesirables', and it's there. (I've also looked into the eyes of the dead, and seen that essential spark gone, but that's another matter.)
Perhaps it's the aspie in me - from just a young child, I paid little attention to such 'unimportant' things like peoples' status or position. There were undoubtedly tons of little signals which I missed, and which helped others to locate themselves in the social matrix, to know who they had to kowtow to, and who they could lord it over. Children, especially girl children from families of no great social status like myself, were pretty near the bottom of that matrix. I was oblivious to all that. I protested the privileges my brothers and father got. I couldn't for the life of me understand why everyone thought boys were so wonderful. I didn't think it remarkable that some of my cousins and schoolfriends were Maori, or think they were somehow 'lesser' human beings for it. And while I understood that adults had power over children, and knowledge and experience I lacked, I didn't see them as intrinsically superior to me because of it. And so on. I have met many other aspies/auties who share the same lack of awareness of social distinctions, the same lack of prejudice.
Or perhaps it's because I'm of the post-war generation. Growing up, the Holocaust and its horrors were very recent history to me, a glaring example of racism gone mad, and of how thinking oneself 'superhuman' actually made people behave in subhuman ways. I'm also old enough - just - to remember President Kennedy, how wonderful everyone thought he was, the hope for a new world he engendered, and the shock of his assassination, which reached us even here in little ole 'Godzone' at the bottom of the world. The 'revolutionary' events and phenomena of the 60s - the Vietnam War and anti-war protests, the civil rights movement and Martin Luther King's assassination, and even the music of pop groups like the Beatles, were the background to my childhood, while events like Watergate and movements like feminism and gay rights and the 'flower power' of the hippies influenced my adolescence. When I was about fifteen or sixteen, I wanted nothing more than to grow up to be a hippie, and when my father sneered at my 'tatty' jeans, I didn't get why. The prevailing idea was that our generation was breaking down old structures, and creating a 'brave new world'. Prejudice was anathema, to be discarded along with other 'old fogey' ideas and social structures.
Or perhaps it's both of these factors acting together - or neither, but simply something that's part of me, of who I am. There are plenty in my age group, and younger, who didn't get the memo about the revolution, and who are as racist, sexist, homophobic, etc, as any of the older generation were. And I know that there are aspies/auties out there who are prejudiced, and who spout that prejudice at any opportunity. I've met some online (thankfully only a few, in a forum I no longer visit) who rant about Obama and immigrants and blacks, or see being gay as a 'sin', etc, etc. They do exist.
So I don't know why it is, exactly, I lack any ability to feel prejudice. All I do know is, I don't understand it, I don't understand anyone thinking themselves a superior type of human being, and I will never, ever, ever support it or knowingly perpetuate it. Ever.