"...we would do well to remind ourselves that it is not acceptable to use animal or geographic metaphors about immigrants."

What great nonsense you do talk, Emma B! We happily talk about crowds flocking to Goose Fair, about protesters being herded into side-streets: but we are forbidden to use "animal or geographic metaphors" about immigrants?

English uses metaphors, you clot: to deny their use in relation to immigrants would merely emphasise the differentness of immigrants, something you apparently can't countenance.