I think, from the nature of the quotes that Rainboy posted, that if you showed this statement to a zoophile they would assert quite boldly the ability and willingness of animals to consent to sex acts (even with humans).
Even many animal lovers (who are not sexually interested in animals) will assert to their pet's ability and willingness to love them.

Dogs are most notable for their frequent initiation of sex acts with humans.

Plus if you are going to discriminate on the terms you have here then you disqualify many mentally or physically disabled persons from the prospects of marriage.

Finally, you have no scriptural grounds for making the distinctions you do in this argument. The animals are not human issue is just not an issue of Scripture. All of your statements here are completely subjective.

As to the subject of Polygamy, I don't believe Scripture ever condemns the practice. The one wife ideal, does not anywhere in Scripture stop the taking of additional wifes or regard it as sinful, illegitimate or adulterous. Only those in leadership are commanded not to do it for the sake of their other responsibilities.

Some non-western cultures survive quite healthily as polygamous cultures with no degradation of the women involved.

Blessings
Cat.