We depend on the world. It's where we buy our groceries, our clothes and our Nintendo games. It's where we earn our livings and where our children attend their schools. The purpose of the family, therefore, isn't to isolate my children from the world, it is to prepare them to live in it. Children will, therefore, continue to be born, will continue to need to be feed, clothed, changed and educated.
Families serve as the main tool for that function.
Some do it well, some not so well, and some scarcely at all. Unless I am badly misinformed, there are no laws mandating that you raise your children thusly. As I understand it, if you and several of your like-minded friends want to raise your children collectively, you are entitled so to do. I do suppose its possible that those who are not part of or who do not agree with the struture of nuclear families may feel at odds with a culture that families do largely define. If you don't want a family, don't start one.