Why is the word being used as a suffix with human, as in human being, instead of creature?
Please answer philosophically.
According to the ODE, being means the following:
3 a real or imaginary living creature or entity, especially an intelligent one: alien beings | a rational being.
If you look at the definition, it says a creature that is intelligent. Since intelligence is part of our DNA, being makes more sense than creature.
A human being isn't a fixed, static state. Or at least, we aren't supposed to be - what we have become now (psychological entities caught in our own past and memories, with memory playing re-playing itself as thought and personality), is sadly far from the human possibility that many human beings in our past have exhibited (Jesus, Krishna, Gandhi, Dr.King, Mr.Mandela, to name very very few). Now, when we say "human being", we refer to something moving, fresh, new, innocent, constantly living and dying every moment. The human world today is largely just a huge bundle of memory and confusion.
I don't think the term human being applies to us anymore - see what we have become. We function primarily out of pain and pleasure (translating into likes and dislikes), constantly within the ambit of thought. We are programming machines to do this - so how different are we from machines? We have emotion. What is emotion, really? Is it not just stickier thought? Thought, that has a deeper impact (from memory) becomes emotion. So, however "great" our thought, it still has no existential significance or relevance whatsoever - i.e., the universe does not know nor care what you are thinking (even if you're Albert Einstein).
So the term human being, while being completely capable of describing a human possibility beyond what we experience in our daily lives, currently, is not an accurate term to describe the human that exists today.
NB: Agreed, not really appropriate for the english stack exchange, but the OP did want a philosophical answer, and it is a very very interesting question regardless of forum.