"It's not a grey area, because removing their kids for holidays changes the nature of the remaining community, and that's neither nice nor fair.
So if you don't want to be part of such a community, you don't have to. Using state schools is not mandatory. "
This isn't how communities work. It is a grey area.
Communities work by people more or less sticking to agreed codes, with leeway on a case by case basis for people who can't or won't.
Communities don't work by kicking people out who struggle with aspects of individual codes. Communities - good, successful ones - work by managing a balance between collective behaviour that enforces codes and a collective degree of tolerance when codes are bent or stretched by individuals.
Yes, in one sense it is harder to teach when pupils are not robots who all turn up at exactly the same time every day and do their homework in exactly the same way.
But in another sense that is what education is- engaging with the whole person and the whole family - and understanding that the absence of a week to go to a cousin's wedding in India comes from exactly the same place as the warm loving family that support the child, want him to do well, and have brought him up from birth to learn to walk, talk, be polite, tell jokes when appropriate, treat adults with respect and treat little ones with kindness. You can't have children without parents and parents deserve respect and support for everything that they, in turn supported by their extended family, do.