Jim,
Good point IF that is the view of baptism. Within Catholicism however, baptism imparts Grace, makes an indelible mark on the soul, creates a new being in Christ. This baptism takes place in one of three ways. First there is standard WATER Baptism which everyone knows about; secondly, there is Baptism of BLOOD, those who, though not baptized, die for the faith; and finally, there is the Baptism of DESIRE, which covers a great many people. Batism of desire occurs some one either wishes to be baptized but can not be for whatever reason, or those who would accept baptism IF they knew it were a requirement.
That's the Catholic view, therefore, given the Catholic view, the marriage also imparts grace, and the marriage ceremony is more than just a public declaration of dedication to a spouse. Further, the joining of two people in sex makes them ONE FLESH, which is why multiple partners are frowned upon. Fornication makes a lie of this unity proclaimed in Genesis and the gospel, and adultery is in direct opposition to the unity of the sex act.
JMHO
Yeru
YERUSALYIM
"Vanity! It's my favorite sin!"
[Al Pacino as Satan, in "DEVIL'S ADVOCATE"]