One can be an environmentalist and an animal liberationist (premise for reductio).
If animals ought to be protected from being killed (because they can feel pain, ect.) then the natural environments in which their lives are at risk ought to be reformed or eliminated (from liberationism).
The natural environments in which their lives are at risk ought to not be reformed nor eliminated (from environmentalism).
Therefore, it is not the case that one can be both an environmentalist and an animal liberationist (from 1, 2, 3).
- Therefore, one can only be an an environmentalist or only an animal liberationist (or neither) (from 4).
This sort of argument was spelled out in greater detail by Mark Sagoff, and it is an interesting one. Given their criteria of value (the ability to feel pain gives one moral status), animal liberationists ought to intervene in ecologies where sentient creatures are naturally harmed. That is to say, there is no good reason for letting such animals die in their natural habitats; indeed, one seems required to act for the same reason that requires one to protect children from grizzly bears–suffering ought to be prevented. Conversely, an environmentalists, who primarily values things like wilderness or biodiversity, has reasons not to protect animals in the wild (unless they are endangered): these environmental goods take precedence over the interests and welfare of animals. Thus, it seems environmentalists are interested in preserving states of affairs that, for many animals, are nasty, brutish, and short.
It’s not clear to me if Sagoff personally believes this, but he seems aware that this sort of argument constitutes a reductio of the animal liberationists position. I tend to agree with this… what does Peter Singer think of lions, tigers, and bears? If anything, premise two seems to be the most vulnerable, and it would be prudent to revise it to say “animals under our care ought to be protected from being killed…” But some justification for circumscribing the animal kingdom this way needs to be given, and it isn’t obvious that it will be compatible with the primary values of animal liberationism.