You're a hoot.
The purpose and effect of making barnyard sex, and any other pornography more accesible and visible is to make it more acceptable, and thereby increase participation in those sorts of things.
That internet porn is a growth industry is a demonstration of that.
There aren't 39,000 barnyard sex sites because no one's interested. Do you doubt that people interested in bestiality would want to be free of fear from legal restrictions?
Why isn't there an unenumerated right to bestiality, as an extension of the unenumerated right to privacy, provided a man doesn't offer his favorite ewe a cigarette afterwards?
How do you know that's the purpose unless you're involved in the production and distribution of those materials? You're making a presumptive allegation.