"If all kids were brought up with the same sort of discipline, you would not need your "tiny classes with no disruption"... because there would be no disruption. In that sort of environment, kids learned that your outlook in life would be limited, if you didn't value education, and parents taught their kids that."
Because all children do exactly what their parents teach them to do and there are no children with emotional or behavioural difficulties which can't be fully pinned on inadequate parenting? 
I have two disruptive children and one who is completely compliant. How did that happen when I bought them all up the same way?
One of my children has ASD. He's bright and loves school. He's also an extremely nice and responsible child, but he struggles with relationships and gets into conflict with other children which disrupts lessons. He's in a class of 31 children and has no allocated support. There are two other children in his class who have special needs and no allocated support.
Whose fault is it that there is regular disruption in my ds's class? My ds's? Mine? The teacher's? The school's?
What about my dd? In year 11, she's spent the last 3 years in constant threat of exclusion at her comprehensive. She has two loving and involved parents with a strong work ethic and high expectations of her, but despite a great start (she breezed through primary without a whisper of a problem) she has bought her teachers and us to the brink of despair with her behaviour.
Having a child who has had a difficult time at school has humbled me. It's been so difficult DESPITE the fact that we are a solvent and educated family with strong social support and a knowledge of the importance of boundaries and respect.
In the end the children who need the most help - for whatever reason - who get the least. The wealthiest and best supported and most high functioning and able children get more than double the amount of money spent on their education as most children in state schools.
That is fundamentally wrong and I can't see any ethical justification for it at a social level.