I've enjoyed reading the posts in this thread from the past few days. I must say that I've a great deal of respect for Andreas' question, and look forward to further discussions about the topic.
A few things to bear in mind:
Firstly, there is a difference between abstaining from something (like meat) 'out of abhorrance of it' - which is the language used in the canon mentioned earlier in this thread - and abstaining for cause of concern, care, love, compassion, ascetic growth, etc. The canon condemns the abstaining of several things on grounds of an 'abhorrance', indicating above all a (wrong) belief that such a thing is intrinsically wrong or evil (this canon is most often quoted in reference to marriage and/or sexual relations, against those who argue that all such are evil). The point of the canon is that what God creates cannot be abhorred as evil, since God creates only the good. An so the apostolic canon:
'If any Bishop, or Presbyter, or Deacon, or anyone at all on the sacerdotal list, abstains from marriage, or meat, or wine, not as a matter of mortification, but out of an abhorrence thereof, forgetting that all things are exceedingly good, and that God made man male and female, and blasphemously misrepresenting God’s work of creation, either let him mend his ways or let him be deposed from office and expelled from the Church. Let a layman be treated similarly.'
The focus of the canon is clearly on the 'blasphemous misrepresentation of God's work of creation', rather than on the simple act of abstaining. In point of fact, the canon explicitly provides one context in which abstaining from such things is good and holy: namely, what it calls 'a matter of mortification' - since mortification, as part of the ascetical project, is ultimately an act in reverence of creation (through transforming fallen man into a true relationship with it), rather than a dismissal of it.
One might certainly ask whether abstaining from the eating of meat on grounds of the glorification of God's creation - of diminishing suffering, which ultimately is always caused by human sin; of regaining the intimate relationship with the animal kingdom that is evidenced in the lives of the saints and the patristic writings on Eden, etc. - is not in fact a perfectly reasonable justification for holy abstinence.
Secondly, the passage in the Acts of the Apostles (Acts 10.11-15, etc.) regarding St Peter's vision of the many 'unclean' animals, needs to be read for its authentic message, and not as a tract on vegeterianism. The point of that vision, as seems to me very clear in the text, is that man is not to cast as 'unclean' (i.e. unholy, impure, untouchable) that which God has created, and which by his own self-sacrifice he has redeemed, as he redeemed the whole of creation. Man is not to take the ox which God has made and say 'good, clean', but then to take the pig which God has made and say 'foul, unclean'. So St Peter hear's God's voice: 'What God hath cleansed, that call not thou common'.
It seems to me that this speaks very much in the same vein as the apostolic canon: it's primary concern is that humanity not seek to debase God's creation by insisting that aspects of it are 'common' - debased, dirty, foul, evil, etc. All that God has made, all that God has redeemed, is holy. Which is precisely why - to refer to the psalm verse Andreas has already mentioned - we can sing at every matins service, 'All creation hymns thee...', 'Let everything that hath breath praise the Lord...'.
Thirdly, passages such as St Paul's comments on judging a brother with respect of what he eats, should be taken as just that: comments on judgement.
It seems that the real question is: why does one act? I rather do believe there is good evidence in the patristic and monastic contexts especially, for upholding a positive view of refraining from eating animals, if done for the right reasons.