There are 7 billion people in the world. Those posters who make the assumption in their posts, that "of course" everyone agrees with their position that Prop 8 was wrong, might want to reflect that probably less than 500 million, or less than 8%, agree with them.
The debate that such posters believe has already been settled, will be going on for a long time.
You think that we haven't considered the relationship between morality and popular opinion, and that we should give more weight to popular opinion? And that if we did, we'd see it makes a better basis for morality than models that highlight equality and enumerated rights?
Not at all; however I think there is, how shall I say it, "whistling past the graveyard"? "wilful blindness"? when it is expressed as if it is a majority opinion among humans.
It is like the anecdote about the woman living in the cocoon of NYC's Upper East Side, who said after Nixon's landslide win of the presidential election of 1972 "I can’t believe Nixon won. I don’t know anyone who voted for him."
The debate that such posters believe has already been settled, will be going on for a long time.