I was going to write a post on animal rights a few months ago but thought better of it. I changed my mind and fluffed up what I had written in order to supplement (but not invalidate) the discussion initiated by Jason over here.
Environmentalism and animal rights should remain separate groups. Their interests, though sometimes related and even mutually beneficial, are just as often too disparate for a harmonious union. For example, hunters can make powerful conservationists (conservation being a major branch of environmentalism), but hunters and animal-rights activists mix worse than oil and water.
This article makes mention of the hundreds of thousands of goats that have finally been eliminated from the Galapagos Islands. By eliminated I mean: they were shot. Had an organized and well-funded animal-rights campaign arisen, accomplishing that task might have taken much longer, or cost a great deal more. Or it might not have happened at all. I use these goats as an analogy for the horse roundup mentioned in Jason's article. Both species of domesticated animal are the result of many thousands of years of genetic engineering by human beings to produce an animal of use to them. Neither has a place in the wild. The ecosystems they evolved in are human-generated.