"This man is not moral."
Translation:Ο άντρας αυτός δεν έχει ηθική.
You are right, but "άνθρωπος" has a universal significance that the word "person" does not have. For example:
mankind = ανθρωπότητα
So, "this man is not moral" could also be translated as "ο άνθρωπος αυτός δεν έχει ηθική" if you want to stress the lack of "universal" morality, that ought to exist.