Yes, in their respective countries they can do that all they want, but if they are going to move to a different country (usually due to war) they need to abide by the cultural norms in that country. This becomes very conflicting when Muslims or other religious groups immigrate to countries that have been homogenous for most of their history. They immigrate and start to demand that schools or public institutions accommodate their traditions and beliefs. This is what the author is essentially trying to get at.