I think you've missed the main implication of my response. I'm claiming that our only impetus for inventing the concepts of "good" and "bad" or "right" and "wrong" is to describe things that we like and want (i.e. that make us happy) and the things we don't like and don't want (i.e. that make us sad or afraid), and that, therefore, the only way to measure something as "good" or "bad" or "right" or "wrong" is by it's affect on our happiness.

Surely you can see the obvious, essentially tautological truth in that.

And assuming you do, then the next thing to realize is that it doesn't matter whether trying to make everyone happy has inherent challenges. Happiness and sadness are literally the only way to measure good or bad, and are therefore literally the only option we have in deciding between right and wrong, despite what challenges we might face in doing so. Providing food, shelter, and a place in society is also challenging, and yet that challenge is something that most people easily accept as being a major goal of any community. All I'm really driving at is that happiness is the even deeper reason behind all of those other more openly acknowledged goals.

The question, then, is how do I / you / we determine some ground rules for a society that we think offers the best chances of happiness for as big a variety of people as possible?

And in the case of your specific example, the answer is that, unless the minority's actions are having a direct and inevitably detrimental effect on the majority's happiness, then the majority should not have any grounds to prevent the minority from doing what they want. A minority of people having same sex partnerships does not affect the majority's happiness in any measurably comparable way to the unhappiness that would be caused by preventing the minority from having relationships with whom they want. And so the happier road is obviously to allow and recognize gay marriages.