Why do we marry? (Jungtzu Lin)

Why do we have to marry? If we love somebody and want to spend time with him/her, we need to marry legally?

As legalized marriage is considered as social system which maintains social norm and morality by keeping kinship and family, reputation and honor of family become important factors to be considered in order to decide marriage partners especially in conservative society.
If so, what is wrong to marry somebody whom parents choose for daughters? Of course, I believe that women as well as men should be protected under equal rights, and women should get higher education. However, as Ms. Sultan said, “the core issue was really a different philosophy of what it means to be Afghan and what it means to be Americans,” we cannot judge their way of marriage.

Moreover, we take it granted that we have not only the right to decide whether we marry or not, but also the right to choose a partner. However, in reality, we are inclined to choose a partner who is desirable for parents in terms of economical and social status.