I responded to Post 8407 in which SV wrote: "How can anything that happens among consenting adults in the privacy of my home affect you, in any way at all?" SV didn't qualify that statement in any way. It makes no reference to homosexuality. Consequently, your question is moot.
It could, indeed, apply to my observation inasmuch as SV didn't specify the sexual orientation of "consenting adults." If he had homosexuals in mind, why didn't he write "homosexual consenting adults"?
Okay. If we grant your premise that some things which consenting adults do in their own home
does affect others and should be regulated by law, there's still another step in the chain of logic that needs addressed.
How do we decide which things should be regulated? On what basis is homosexual marriage one of the things that should be banned?
Playing devil's advocate, I can see some logic in saying that if personal freedom is important, individuals should have the freedom
not to do things: not to sell their home to black or interracial or gay couples, not to let blacks or Asians or Jews or gay couples eat at their restaurant, not to hire any gay couple who claims to be legally married, and so forth.
The problem is that allowing that kind of personal freedom undercuts other personal freedom. If gay marriage is made legal but private individuals can band together to prevent such married people from getting jobs, buying homes, etc., then gay people really don't have the same freedom to get married as others.
The tide shifts. In the US, I remember when smokers argued that they should have the personal freedom to smoke wherever a business-owner allowed and non-smokers had no right to infringe on that right. Nowadays, it's the opposite: states have told business owners that they must ban smoking, whether they want to or not, and most people are okay with the laws.
Similarly, the tide shifted on racial and religious discrimination. "No Jews" or "no coloreds" used to be a free choice of business owners or home sellers. Now, it's the opposite: the rights of Jews and blacks trump others', in most cases. (You can still throw a private party and disinvite whoever you want.)
I'm expecting gay marriage to be similar. The tide has shifted. Society wants it to be acceptable, not just de jure but de facto, which means others
will lose a few rights. But they'll survive, just as whites did when blacks moved into their neighborhoods or married other whites. And Mormons--the ones who abide by the articles of faith, at least--will comply with the changing laws and survive too, because they "believe in being subject to kings, presidents, rulers, and magistrates, in obeying, honoring, and sustaining the law."