Many people are like that, its instinct. Children just lack the social training to build the inhibitions to disregard it. It stems from our fear of difference.
See, discovering agriculture was a huge accident and caused us to build this exponential momentum of technology growth. We've developed technologically much, much faster than our brains have been able to match evolutionarily. One of our technologies are massive, functioning societies, allowing us to experience different lifestyles and culture within the safety of an established social community. This, on paper, is a good thing because we are able to learn and understand each other in a safe environment.
But, because our brains are still socially wired to live in small, close-knit tribes, we fear difference. In the distant past, a disease from a neighboring clan, poison from a new fruit, trusting a wandering stranger not to steal from/kill you, even something as different as building the fire in a different way, threatened to thin out or completely wipe out your family or your tribe or your clan. So we came to fear things that were different than what we were used to. You name it. From skin color to culture to size and shape and everything in between. It's why you get anxious when the lights go out (I could see, now I can't, something's different), why people are racist, sexist, ageist, and homophobic. And to start relating to the initial point, it's why people bully each other. It's why people demonize being "weird," why peers pressure you into doing drugs or dangerous or illegal behaviors, and why everyone pushes for conformity. If you look different or want to do different things, it invokes anxiety in others, and our savagry comes out to defend against the threat.
This can be obvious in cases like these
https://goo.gl/rLra2E
Or it can be less obvious, subtle like the downvoters for that 1000 wins post. Maybe its jealousy, maybe it's trolling, but they're not at 1000 wins and this person is so fuck them.
It's human nature; I'm sure you've felt these ways before when you were younger and didn't know any better, and if you have children they'll feel the same way. I believe everyone can benefit from therapy, but instead of wasting the money on therapy, you could just teach them better. That's what I did for my 9 year old nephew after he just playfully and non-seriously said his sister couldn't play softball because she was a girl. Instead of getting angry or disgusted I let him know how people worked (in a briefer spiel than this post) and taught him that being different, whether physical difference or different choices, is part of being an individual and should be praised, not shamed.
