Because it does lol. There is a definite hierarchy in living things, and trying to say that animals aren't below humans is incredibly stupid and simpleminded. This is pretty much as close to objective as an opinion can be.
in the hierarchy of the environment ya obv, that's the natural order and it makes sense for people to follow it. it also makes sense for people, as highly intelligent human beings that are capable, to develop moral codes that might alter how they view that natural order
more to the point: something being a product of natural order doesn't make it objectively more or less moral, and moreover, no morality is inherently superior.
edit: to be more precise, calling someone an idiot implies that they're somehow inferior, not to mention dismissive if it's because of a subjective belief