Why is it so important to society that marriage be preserved...?

I stumbled across a Q & A that was featured in the Catholic Update newsletter in 2004. To go to their article "Between Man and Woman: Questions and Answers about Marriage & Same Sex Unions", please visit: http://www.americancatholic.org/Newsletters/CU/ac0304.asp.  The whole article was excellent, but thought this question and the answers were simple, yet significant.

"Why is it so important to society that marriage be preserved as the exclusive union of a man and a woman?

Across times, cultures, and very different religious beliefs, marriage is the foundation of the family. The family, in turn, is the basic unit of society. Thus, marriage is a personal relationship with public significance.

Marriage is the fundamental pattern for male-female relationships. It contributes to society because it models the way in which women and men live interdependently and commit, for the whole of life, to seek the good of each other.

The marital union also provides the best conditions for raising children: namely, the stable, loving relationship of a mother and father present only in marriage. The state rightly recognizes this relationship as a public institution in its laws because the relationship makes a unique and essential contribution to the common good.

Laws play an educational role insofar as they shape patterns of thought and behavior, particularly about what is socially permissible and acceptable. In effect, giving same-sex unions the legal status of marriage would grant official public approval to homosexual activity and would treat it as if it were morally neutral.

When marriage is redefined so as to make other relationships equivalent to it, the institution of marriage is devalued and further weakened. The weakening of this basic institution at all levels and by various forces has already exacted too high a social cost."