There is a very simple meta-argument: whatever your argument is for giving value to humans, it will also be strong enough to show that some non-human are also valuable, due to a partial overlap between humans and non-humans in all the properties you might credibly regard as morally relevant.
How about in-group affiliation with members of your own species?
Do you really believe that, when a creature suffers intensely, your reasons for relieving this creature’s suffering derive from the fact that you share a particular genotype with this creature? If you were later told that a being whom you thought belonged to your species actually belongs to a different species, or to no species at all (a sim), would you suddenly lose all reason to help her?
How about in-group affiliation with members of your own species?
Do you really believe that, when a creature suffers intensely, your reasons for relieving this creature’s suffering derive from the fact that you share a particular genotype with this creature? If you were later told that a being whom you thought belonged to your species actually belongs to a different species, or to no species at all (a sim), would you suddenly lose all reason to help her?
I don’t, but I don’t dismiss the possibility that other people may; I’ve certainly known people who asserted such.