This logic of consistency which you are using to interpret and extrapolate the law is quite rediculous. Unless you equate the law with right it doesn't make sense to insist on extending the law as far as consistency permits. To me it seems to be a relatively simple matter to acknowledge that the raising and killing of animals of for consumption (primarily in the form of food and clothing) is strongly culturally engrained and for the most part has been accepted throughout the recorded history of human civilization. Furthermore, animals and such derivative products are incorporated into various rituals (the sacrifice, the feast) and in many cases are attended by an overlay of symbolic meaning, e.g. of wealth, luxury and abundance. If we add to this not only red meat producers, but also the extraordinarily powerful companies whose products depend on red meat - I need only cite McDonalds here - and their lobby groups it is easy to realise that the likelihood of significant (i.e. doing more than adding 0.2 m^2 to the size of a cage) legislative change restricting or prohibiting the slaughter of animals is very low.
If we acknowledge the historical-cultural nature of our treatment of animals, and the current economic forces which ensure the perpetuation of this form of treatment, I fail to see how one can reasonably argue that from the law concerning slaughtering we can conclude that bestiality ought to be permissible. Given your 'pro freedom' stance I'm sure there exist dozens of laws which restrict freedom to which we could apply your 'consistency argument' for extension of the law in order to further restrict freedom. In such cases I'm sure that you would realise how faulty this form of argument is.
It is one thing to say 'I permit the killing of animals' therefore, a fortiori, 'I permit bestiality' - I can certainly see the validity in this form of subjective moral reasoning. But I think it is rediculous to reason that 'it is the case that current legislation permits slaughtering' therefore 'we ought to extend the law to permit bestiality'. Firstly the law is not necessarily right, and at best, I would suggest, is an imperfect approximation (no doubt a select few philosophers of law would disagree with me here). Secondly, if a given law is acquired through tradition and longstanding cultural practice and is resistant to change, e.g. on account of cultural rituals and economic forces, then it is possible to accept the continued existence of a law, in a realistic fashion, whilst denying its ultimate claim to right or further extension.
