Separatism is created by disparity. It's the divide taught from a young age. "You look like this, so this is your place" "You can draw or you can kick a ball, so you go this way and you go here." The exploration of our interests gives us a sense of belonging but also limits the stories we tell ourselves. In addition, to be pigeonholed into a particular grouping is how we are defined, and essentially kept in that limitation.
What is ingrained in our egos can make us incredibly unkind to ourselves. It makes us comparative and lacking understanding. From here, we diminish our light or amplify it, by that I mean suffrage from either inferiority or superiority complex, and the underlying competition of life begins. Based on our self-sovereignty and courage, we can see beyond these imposed limitations, but it is probably safe to assume that even the most defiant of creatures *ahem* can fall complacent to this divisive nature.
In my experience, the inclusion of others often led me to feel uneasy at best. It has been the understanding of intuition that I embody that is seeing the good in others doesn't necessarily mean that everyone needs to have access to everything you offer. My lesson in inclusivity is that I can adapt to most environments, but if I feel protective over something, it is generally my intuition telling me that I am not safe in my surroundings. I have spent a lot of time in this state of analysis, still wanting to create a sense of unity, but realizing my self-sacrificial tendencies to make others feel good caused me to forget about myself.
Realizing this and finding that balance has been imperative for me to understand separatism. It's how I have felt both inclusivity and exclusion throughout my life that created that disparity within me. So on one hand I want everyone to have a chance, but on the other, I know the situation is not right for me. Its the process of lowering our standards or working to believing that others are akin to us that we can see the commonality between humans. We all just want to belong. But you need to know who you are and what you want to belong to first and why.