Well, my reply to you was badly stated, in that it implied a commitment to relativism, which I do not advocate. A better statement of my position is in post 296: if a moral claim is supported by the best reasons, then it is one we ought to recognize, even if people in fact don’t recognize it. To give a cliched example, in 1830 there were good reasons to regard slavery as immoral even if as a matter of fact most people didn’t recognize those reasons.
As I said, for reasons related to the tragedy of the commons and the free rider problem in economics, there are good reasons to regard overuse of resources as wrong, even if as a matter of contingent fact many or most Americans don’t recognize that owning a McMansion or having 18 kids is wasteful of resources (i.e., they don’t recognize the factual claim) or don’t know that wasting resources is wrong (i.e., they don’t recognize the moral claim).
That’s fair enough. There’s lots all of us can do to cut down on our resource use. As you mention, meat consumption is a very wasteful way to nourish yourself (and unhealthy, to boot), so most of us could stand to reduce the amount of meat we eat. A lot of it is asking not “At what level should I consume?” but “In what ways can I consume less?” Because you are right, I don’t know what level of consumption marks the dividing line between wasteful and non-wasteful (although as I continue to claim, I don’t think this admission prevents me from making claims about extreme cases that are far from wherever the dividing line would have to be drawn).