Have you ever heard someone make a claim, and then when asked to justify it, the person takes a second to make up with something? If the person doesn't already know the justification, then what logical basis does the person having for believing the claim? Have you ever heard someone ask something like "What is it that makes us human?"? Often, the person asking isn't quite sure, and the other people around all agree that there is something that separates humans from all else, yet often can't put their finger on what that difference is. Now, if they aren't sure, what logical basis do they have for believing that there is such a difference, such a defining characterstic? I think that such thinking leads to many half-assed ideas (especially, but not only, in the case of anthropocentrism) that fall apart in the face of logical analysis. This is that rationalization defense mechanism that we all learn about in Psychology 101. It's a sad thing that leads to many injustices. If you don't have already have a justification for your belief before having it, you should question whether the belief itself is valid, instead of scrambling to come up with a justification...right? If you have such a belief about humans and a justification for it, you should ask yourself which came first. If the belief came first, then you should question the belief. If you have the belief and no justification, then you should question the belief.