I wasn't aware that I implied that self-gratification is a denial of the natural order, and if my post can be construed that way, I'll have to explain myself differently.
Self-gratification is the natural end of same-sex acts. That is, same-sex acts are ordered toward self-gratification.
Procreation is the natural end of opposite-sex acts. That is, opposite-sex acts are ordered toward procreation.
One can only make the case for parity between opposite-sex acts and same-sex acts if one denies that procreation is the natural end of opposite-sex acts -- that is, if one denies the natural order. IMO, such a denial is completely unreasonable.
I buy it, but only to a degree. Lots of men and women voluntarily get sterilized once they've decided to stop having children. Sex then becomes strictly an act of self gratification, doesn't it? The same might even be said of straight couples that have sex while using birth control devices. My point is that self-gratification is another legitimate end of sexual relations.