We shall now proceed to the next statement of Celsus, and examine it with care: “If in obedience to the traditions of their fathers they abstain from such victims, they must also abstain from all animal food, in accordance with the opinions of Pythagoras, who thus showed his respect for the soul and its bodily organs. But if, as they say, they abstain that they may not eat along with demons, I admire their wisdom, in having at length discovered, that whenever they eat they eat with demons, although they only refuse to do so when they are looking upon a slain victim; for when they eat bread, or drink wine, or taste fruits, do they not receive these things, as well as the water they drink and the air they breathe, from certain demons, to whom have been assigned these different provinces of nature?”
Here I would observe that I cannot see how those whom he speaks of as abstaining from certain victims, in accordance with the traditions of their fathers, are consequently bound to abstain from the flesh of all animals. We do not indeed deny that the divine word does seem to command something similar to this, when to raise us to a higher and purer life it says, “It is good neither to eat flesh, nor to drink wine, nor anything whereby your brother stumbles, or is offended, or is made weak;” and again, “Destroy not him with your meat, for whom Christ died;” and again, “If meat make my brother to offend, I will eat no flesh while the world stands, lest I make my brother to offend.”
Source: Against Celsus (New Advent)