"Exceptional", in this sense, means something which is objectively removed from others of it's sort, in this case, humans from other life-forms. It is the notion that humans are "above" other life-forms, and so liberated from the burden of moral responsibility towards them.
Moral responsibility can only be shared with other members of the same community. Morals involve both duties and obligations which must be
agreed upon, and have no meaning outside a community. It can be an objective one, of human beings, or an imagined one involving ancestors or gods, but they must always be conceived of as a community. Even when groups of humans "respect" specific animals, they do so not out of moral obligations or negotiation with those animals, but out of a negotiation and understanding
among the humans who compose the community. Each individual is morally responsible
towards the community of humans which made the rules, not towards the animal which is protected by the rules.
As for being above other life forms... those others which cannot communicate with humans are free to contest mastery of the planet from humans. They
are contesting it, from bacteria to large carnivores. And in this humans look out for their own interests, as they should.
Can children "discuss civilised issues"? Can the severely developmentally disabled? I think that your boundaries are tighter than you intend.
You started this discussion asking what made humans,
as a species, special. I've shown you what makes humans, as a species, different, and why they can only relate with other humans. Now you're trying to invoke examples of
individuals within a species, be it one gorilla or special cases of human children or idiots, as alleged exceptions. You've had your goal with this thread frustrated (which, as far as I could see, consisted on making people believe that humans should not treat other animals differently) and refuse to admit it.
These individuals are still part of a larger species, and all I said about species and the insurmountable barrier of communication which puts those apart stands. These individuals are classified together with their species for most purposes, for obvious reasons (same species!). But I do remind you that we don't let children vote on political issues , or let idiots do pretty much anything unsupervised and do not take them seriously. You're just adding to the strength of my argument that lack of communication is the barrier making humans exceptional.
Also, that merely explains why an exceptionalist attitude develops, it does not act as a defence of it.
Facts of nature need no excuse. Humans are a different species, and cannot communicate and negotiate with others. Things are as they are.
Or do you think that gays, for example, should make up excuses for what they are?