Imagine a relatively perfect world, where all animal advocates and vegans have read your book and adopted your views. Under this best-case scenario, how do you see society evolving over time? IOW, what is your optimistic view of the future?
It's really hard to say. I do think that if all animal advocates and vegans put the research discussed in Change Of Heart into action, we as a movement would gain ground much more quickly. I think we'd all be focusing on the issues where we can do the most good (primarily farm animal issues), and methodically making small but important improvements in our tactics, messaging, and general approach. I do think that the percentage of vegans, vegetarians and semi-vegetarians is going to continue rising for awhile; I do think that we will see bans on the worst factory farming practices; and I do think we'll see strengthening of all types of welfare laws and increased general social concern for protecting animals. I also think some fringe uses of animals will be banned or phased out over time (like animals in circuses), and that eventually technological advances will lead to a sharp reduction in animal testing and (when in vitro meat works out) meat consumption. I think the research in Change of Heart can help speed up some of these processes and save more animals more quickly.
That being said, I'm not particularly optimistic that human beings are going to voluntarily change their lifestyles enough to prevent serious environmental breakdown and the harm that will cause and is already causing, at least in the short term, for animals (particularly wild ones). Ultimately it's not just our diet but our whole consumption-heavy way of living and our industrialized society that hurts animals. Billions of animals suffer and die in factory farms each year, but many also die from other human activities and billions more will not be able to be born because we've taken over and decimated so much of the land. So I'm optimistic that change will happen for the animals in terms of our use of them for food, clothing and so forth, but not very optimistic about the situation for animals from the wider perspective of industrial civilization as a whole.
But that's a somewhat separate issue. None of us can predict the future, and even if some catastrophic climate change happens down the line, that doesn't mean we should ignore the suffering going on right now, suffering that we can prevent. So that being said, let's get leafleting!