The major difference that would arise here is that our lives would be dictated by whatever the government happens to think the appropriate vision of family life is. It would be a better world if people would think of family relationships first. But if government tried to base our rights and obligations on this, we would be liable to end up with some sort of tyrannical government that tried to control every aspect of our lives.
Let us look at some examples.
- On a relatively benign level, divorce might become illegal if the government decided that the need for stable families overrode people's right to decide what kind of family relationships to be in.
- To take it farther, might the government start to monitor what we spend money on? If I had a midlife crisis and wanted to buy a fancy car, might the government step in and tell me I need to save that money so my kids can go to college?
If we are going to say that government should think of people's rights and obligations in terms of their families, it gives the government the right to poke into every part of our lives, telling us how to live in a way that (they think) is best for our families. This could easily become a totalitarian system.