I begin with human psychology and then see what we can say about ethics.
Since for me moral demands necessarily flow from human psychology, I don't think we can be obliged to do something that we are not motivated in any way to do. In other words, I'm an "internalist" about morality.
People who go around saying that it is wrong to fly and to eat meat are not so much making appeals to us from within our shared morality, but engaging in something more like "persuasive definition." They want us to look at the world and ourselves in a different way. Someday these prohibitions against flying and eating meat may be written into our moral psychology, but it will only be after there are viable, widely shared alternatives that are beginning to be widely adopted.
I take seriously the idea that we are African Apes who (at least for the moment) dominate the planet, but our psychology is pretty much what it was when we were living in small groups on the savanna.
