What (if Anything) Is Wrong with Bestiality

Ever since Peter Singer suggested that bestiality was morally permissible not too long ago, I've been puzzled by why its not completely obvious to most people that bestiality isn't wrong.  Sometimes it just takes someone pointing out the obvious to stir the pot. 

Neil Levy defends Singer's point that bestiality is not wrong.  He writes:

Thus, though there is nothing immoral about bestiality, it might nevertheless be irrational for us to cross this boundary.  It would be difficult to do so while yet retaining a strong grip on our identity.

So here's some context.  Levy spends most of his paper responding to possible moral objections to bestiality:  it is a perversion, there is no consent, animals have a lower cognitive ability, it wrongfully utilizes animals as a means to an end, it inculcates vices in our character.  He rejects all of these arguments.

But then, he switches gear and talks about our identity as a species.  We determine who and what we are by the limits of our abilities, upper and lower.  He writes:

In fact, both sets of limits, upper and lower, are in part definitive of humanity. My suggestion is this: The set of limits definitive of human life contains elements from many different sources. Some of them, like the limit represented by human mortality and by our physical bodies in general, are given by nature.... Others, however, are cultural limits. They are the products of the collective imagining of a people. They are, however no less identity constituting for all that. These two sets of limits are nively captured by the word "humanity."

So as a people, we can define ourselves by the natural limits on our bodies and socio-cultural limits that we impose on ourselves.  Good so far.

But our lower limits, which are largely culturally defined, are also identity constituting.... if we cross our upperbounds, we will cease to be human, becoming something different and not necessarily better.  If we cross our lower limits, a similar fate threatens.  To transgress this boundary might be to move to another form of life, in which characteristic human activities have no place or are transformed in ways unimaginable from here.  This might be a limit we cannot cross while yet retaining our sense of who we are.

This seems pretty flimsy.  If our lower boundaries, in this case, bestiality, is culturally defined, then why must this definition be the "correct" definition?  Levy says we have no real reason to think that it is.  These boundaries are flexible, like he states above.

...To the extent that someone engages in bestiality, she will find it harder to retain a grip on her identity as a full member of our community, and we will find it harder to admit her to full membership.

So if we take this position seriously, we might be able to say something like, homosexuality is outside the identity of humanity, and so we should avoid homosexuality because we might not retain our sense of "humanity."  Levy has a reply:

...We needn't be scared of the prospect of  a new communitarian homophobia.  Arguing against homosexuality that it represents a crossing of a signifcant limit places any prohibition against it precisely where it ought to be: in the open, in the realm of public and democratic discourse.  When we realize that the taboo is socially defined, we can begin to assess its costs and its benefits; Given that a taboo against homosexuality would seem to impose a major cost upon a significant minority of the population, I suspect that it would not long stand such public scrutiny.

So because social taboos against homosexuality impose a major cost (sexual and social freedomsI would imagine) on homosexuals, it wouldn't stand public scrutiny.  Wouldn't a taboo on bestiality do the same for those who wish to engage in it?  After all, Levy just finished saying that we would find it hard to admit these people full membership in what we call "humanity."  And for what?  A socially defined lower bottom floor of what makes a person part of humanity.  This sure sounds an awful lot like: "Most people really don't like it."

But wait:

This is not to say that we must retain the taboo against bestiality.  The limits which define our humanity, in the sense here at stake, are, by nature, contingent and shifting....  If this i the case for our upper limits, which are importantly natural in origin, then how much more is it true with regard to the culturally defined lower limits?

Clearly, they would have to be MORE true right?  Surely its much harder to make someone live 110 years than it is to say that homosexuals should be respected. 
Levy finishes with:

Nevertheless, if these considerations are correct, this is not a decision to be made lightly.  To redraw the map of our limits, at the bottom as well as at the top, is to set for ourselves new boundaries within which human life will take on a new shape.  Perhaps Kant ws, at least in part, right about bestiality: nothing less than the meaning of our humanity is here at stake.

I don't think this is terribly ambiguous, although it is.  He could be saying, that there is no moral prohibition against bestiality and that because humanity is, in important ways, socio-culturally defined that we can simply decide to say that people who engage in bestiality should not be ousted from membership in humanity, in full or in part.  But I'm pretty sure what he is saying is that we shouldn't change our definitions of humanity because changing the meaning of humanity is well.... wrong?  That can't be right, since there is nothing immoral about bestiality.  Imprudent?  Just something we should think long and hard about? 

What Levy is doing here is manipulating our attachments to "humanity."  To change these definitions suggests that we are inhuman.  And metaphorically these are the lower levels of humanity.  Why aren't these taboos the upper limits of humanity?  Or off to the side somewhere?  It could be that we are busting through a ceiling rather falling through the floor.  Morally acceptable bestial sex may show an elevated concern for the suffering of animals (being careful not to harm animals while we have sex with them) and trying to share with them an intimate aspect of one our highest expressions of love, care, and devotion.

If we change our conception of humanity who knows what we'll become.  Maybe we'll just become more human, just as we did when we stopped owning slaves, made great strides in equality with women and other races, and became concerned about how we treat animals.