Considerable confusions exists on what belongs to the public and what to the private. One usually describes these as spheres. The public sphere is one which the affairs of the state, the rights of the citizens and aliens, the government and institutions of the state are included. People who hold office are held accountable and their private lives are also kept under scrutiny. The private sphere is the where individuals enjoy the freedom to live their lives freely.
However, the private sphere is not a carte blanche in which individuals can do whatever they please. Domestic violence against female spouse/spouses, children and servants are no longer considered a matter of arbitrary exercise of power by men or other powerful members of the family and friends.
One usually makes a distinction between the domain of citizenship and the domain of religion or community. Modern societies place religion in the private sphere where individuals are entitled to practise their faith or beliefs freely; they are also entitled to public practise of their religion but such practice does not mean encroaching upon the freedom or rights of others.
However, among Muslims the distinction between the public and the private is not clear as many believe that Islam is a complete code of life which looks at all aspects of life as an integrated and indivisible whole.
One can note that such conflation of spheres was common even to medieval and pre-modern Christianity, Hinduism and other religions but with the forward march of time societies have tried to separate the two spheres and institutionalize them through proper legal coverage.
Contemporary norms uphold the distinction between public and private but reformers and legislators have increasingly realized that malpractices in the private sphere cannot be condoned. On the other hand, respect for the individual's private life is upheld in law and social practice.
The opinion which currently exists is that privacy is a human right but privacy cannot be an excuse to exploit or brutalize the lives of others.
Consequently living together, same-sex family and other variations are now acknowledged as legitimate basis for establishing social units. Equally one can choose to live as a bachelor or spinster if one chooses to.
At bottom, the idea is to enhance freedom and equality for all individuals - citizens, denizens, aliens and even those who are in a state as asylum seekers or enemy citizens.