Roman Catholic Bishops call upcoming Prop8 decision a "Roe v Wade" moment

One grows tired of the US Conference of Catholic Bishops, who have their cottas in a twist over the impending SCOTUS decision on Prop8.  To refresh, the Court has been asked to determine whether removing the right to marry from lesbian and gay couples in CA is constitutional.

The USCCB has published an insert for Church bulletins claiming that overturning Prop8 would be the same as Roe v. Wade.  Amongst their complaints,

Every child has a basic, natural right to come from and be raised in the loving marital union of his or her own father and mother.

Now, this is the root of their objection and I would like someone to explain it for me, because it is a complete non sequitor.

How does recognizing marriage between gay couples have any effect on the "right" of children to be raised by a mum and a dad?

1) California has already given LGBT couples complete adoption and parenting rights, regardless of marriage.

2)  It is estimated that lesbian and gay couples in CA are raising over 37,000 children, either their own or adopted.

3) They will continue to raise their children regardless of whether marriage is legal.

4) Ergo, the only effect of denying marriage it to prevent those children, who exist now, at this very minute, from having the protections of married parents.