I probably should relate some of the reasoning behind my 'if I think I could hurt someone, I will not do it' stance, because as I was thinking about it last night, I really couldn't think of much else.
The first two schools I attended through 6th grade -- and we're talking about the late 1970s here, into the early 80s at the tail end -- were not what I'd call bastions of tolerance or diversity. Both were Catholic schools. The first (1-4) was pretty much nightmare fuel; there was zero protection from (sometimes very violent) bullying, and they were so genuinely backward they tried to keep someone back a year 'because they were too short to move on to the next grade'. (Not me, but you can imagine why being a short kid in this place was, uh, not fun.)
So my first 'real world hero' -- not someone from a book or a movie or even documentary TV (I was a Cousteau nerd) -- was that student's mother, who came in to read the nuns the riot act about how completely absurd that was so loudly we could hear her all the way across the stone and brick building.
It had nothing to do with race, gender, or any of the 'big bigotries' we think of, but -- hell, maybe the ADD did the usual blender routine on it in my brain, maybe because it was a stupid 'otherism' that affected me as well so it was more personal than something completely abstract would have been -- it was a very early formative example. 'How tall my son is has nothing to do with the capacity of his brain or his ability to learn, and if you're too ignorant to understand that, maybe I should find someone smarter to teach him.' Go Mrs. McGonegal!
It was a low-to-mid middle class school. 5-6 were at an all girl's upper middle class+ school, and it was so much worse. Everyone in the first school save for one student was white; that improved slightly at the second, but to say the experience those students had there was worse would be a profound understatement. I was 'the poor kid' in that group, and the impact of that was similarly obvious. Catholic Mass and sacrament participation was mandatory. The Jewish girl didn't get a pass. The Hindu girls didn't. The latter had parents who had filed a court order to prevent them from being forced to participate and the school forced it anyway, and fellow students shit all over them along with the teachers.
Again, maybe I only saw it -- and other things I won't relate here because they're egregiously awful and I don't want to dump those into a post where they could trigger someone who has experienced similar -- because I was being shit on by the same people, albeit for a different completely stupid excuse to shit on someone.
But I couldn't not see it. I spent a lot of my childhood feeling batshit crazy because the people in authority -- who were supposed to be our role models and the authority figures we could turn to for help and advice and protection -- were behaving in what was so clearly a harmfully nonsensical way. It was not possible to not see that, either.
That's generally what I draw from, along with the observations I've made over the course of my life since then, when I do make an attempt.