Some would say that non-human animals also have moral value.

Some would, but I'm sure this is something about which reasonable people can disagree.

Slaves used to be sub-human. Women were property. Eventually, if we as a civilization survive long enough, our current treatment of animals will be universally felt to be immoral.

It's even worse than that.

It isn't as if slavery doesn't exist anymore. It is not as if women aren't considered property in some parts of the world. Racism. Etc.