Good question. Iago doesn't really get as far as a philosophy of human nature: there is no "what a piece of work is man", speech, or even a "tomorrow and tomorrow and tomorrow". It's partly why Coleridge dubbed his attitude a "motiveless malignity": the play doesn't really reveal what he really thinks.
You have to read between the lines. And I think you're right about his penchant for human-bestial comparisons. Yet I'd go one further: the animal imagery shows how obsessed he is with sex, and all things sexual:
an old black ram is tupping your white ewe...
you’ll have your daughter covered with a Barbary horse; you’ll have your nephews neigh to you...
It is impossible you should see this
Were they as prime as goats, as hot as monkeys,
As salt as wolves in pride, and fools as gross
As ignorance made drunk.
It's a little like that song "Bad Touch" from a few years ago: Iago loves to imagine Desdemona and Othello having sex like animals do, "like they do on the Discovery channel"! It's part of his weird, psychopathic, obsessive manner, which is reflected in the way he clinically dismembers Othello's faith, piece by piece.
So his view of human nature? Perhaps, in one sense, he just sees us all as primal, sexual, instinctive animals.