Are you trying to say that private schools churn out identikit products?
I don't think that school is the only or even the best way of experiencing life's rich tapestry. If your only experience ever of disability is one kid in your class who constantly irritates you, I don't think that that is enough tbh.
In terms of racial mix, my nearest state primary school is a CofE school with primarily white middleclass children with 2 or 3 black children in each class. Ds's class has 3 black boys, 4 Asian boys, 1 Spanish, 1 Greek (both not speaking English at home) and 7 white boys. The parents are all professionals barring I guess a plumber. But the children definitely are of mixed ability.
Looking at social mix is an interesting one. From what I have seen most schools seem to be so local that they represent a very narrow social mix. Eg in our middle class area most of the children are from middle-class home-owning familes, and there are very free chidlren on free school meals. But we have friends teaching nearby in schools in areas with very low home ownership and high FSM take-up (OK I have to put my hands up and say that I don't know any of the parents!). It does seem that even within the state system children from similar socio-economic circumstances end up together.
My own experience has been that we sent ds1 to a playgroup/nursery in an area near to where we used to live. In ds's 2nd year there I was the only first-time mother over the age of 30 (and the only other mother over 30 was sending her fourth child there), and we were the only graduate parents. I think that, wherever they are, children are made aware of differences, and in this situation ds1 came out very strongly with the idea that he was rich. Now whilst I definitely want ds1 to realise that not everyone in the world is in the same position that we are, neither did I want him being "labelled" by his playmates at such a young age. It also became a barrier to his friendships as some, though thankfully not all, of the mothers felt that they didn't want to do playdates. In some respect I can understand it - I was pretty close in age to their own mothers.
Having had that experience I am much happier being in a position where who I am and what we earn isn't an issue that affects the dcs. Yes they still have to learn about life's rich tapestry and where they fit in, but I'm not sure that school is always the best environment.