>> They believe dolphins and whales are sufficiently intelligent to justify the same ethical considerations as humans. I don't have a problem with extending legal protection to dolphins, but I do think that "intelligence" as the criteria is morally problematic, at least if it's the sole criteria. For instance, could a person with Down's Syndrome be denied protection from murder? The Christian worldview holds that hum…
Since nobody seems to have given a straight answer to this, I will. Someone with Down's Syndrome easily counts as an intelligent being, and is not even close to any borderline.
I suppose your question assumes that, since intelligence comes in degrees, any value based on it must also come in degrees. But instead, most people who see personhood this way believe in some sort of threshold above which everyone deserves equal protection.