Interesting thread. Lots of 'eel wriggling' going on.
It is forbidden for a monk to eat meat if:
1. One kills the living being by one's own hand
2. One urges another to do it
3. One grants permission to another to do it
4. One speaks in praise of killing
As I understand it, Devadatta (the jealous relative and disciple of the Buddha who tried to injure and kill him) split the Sangha over the Vegetarian issue.
He wished the Buddha to state that eating meat was completely wrong and the Buddha refused,even knowing that the cost would be splitting the Sangha.
Although the Buddha thought that Vegetarianism is the preferred manner of eating, he resisted making it compulsory for monks, who are allowed to eat meat as long as they are unaware that the specific animal was killed specifically for their benefit. From the Buddha's perspective, vegetarianism is connected with extreme forms of asceticism, which he wants to avoid.