The problem is that for almost any feature of humanity that you can name, whether it's the ability to suffer, whether it's the capacity to reason, whether it's having lives that can go better or worse, there are at least some other non-human animals that have all of these features as well. So to exclude non-human animals from the range of moral concern but to include all humans, just seems morally arbitrary.

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.

There'll come a time when airplanes are much more efficient when it comes to producing lower levels of greenhouse gas emissions, there'll come a time when we'll be able to offset those emissions much more effectively than we do now. But alas at the moment, flying airplanes is really one of the least defensible things that we do and it's one of the things that I indulge in quite frequently, alas.

Attitudes are changing very quickly.

Aristotle thought that humans are rational animals and Hobbes thought that we act on the basis of rational self-interest. If only! It's not that we never do these things, it's that they are hardly constituative of who and what we are.

The Paris climate conference in December, 2015 was a recognition that countries bring their climate policies to international meetings rather than create them during the negotiations (much less do they receive orders from the international community and then go home and implement them).

Increasingly both environmentalists and animal ethicists recognize the enormous destruction caused by animal agriculture.