Quite easily, given that one is an artificial environment where the participants are forced to conform to certain roles and social norms.
Such structures of dominance and bullying aren't exactly unknown, in England in the fee paying school system there was this https://en.wikipedia.org/wiki/Fagging.
The face people have to their family is not going to be the one they put on when involved in the "Caste system".
Link didn't work, here should be the correct one. https://en.wikipedia.org/wiki/Fagging
Obviously the "Caste system" is more brutal, but anyone from the UK will be aware of similar hierarchy structures that such were found in closed environments like public schools. If you haven't seen the film "If...." which was made in the 1960's it focuses on this structure in a fee paying school, rape of those that were "fags" to their superiors (sorry the term is offensive, but that was what such a role was called) as is happening in this manga.
When is Azusa gonna catch a break around these freaks? It's like the whole notion of just being a "kind" person has completely disappeared from these guys dictionary, I mean how can every single one of them have two faces, one for school and one for their family?