I was vegetarian for several years, and vegan for a brief period. While my reasoning was not as coherent or sincere as that expressed in the OP's quote, it was essentially similar: avoid unecessary cruelty.
Having done a lot of thinking, experiencing and "knowing" between now and then, my diet has changed to reflect my changing view of what is fundamentally right. I view the selected Ahimsa quote as corrupted/false religion, i.e, religion that no longer transmits truth because it has been diluted by "purely human" (as opposed to human but also "more than human") interpretations of reality.
"The meat of other animals is like the flesh of one's son. That foolish person, stupefied by folly, who eats meat is regarded as the vilest of human beings."
This quote is partially correct, but marred by reactionary moralism. Eating the flesh of an animal IS exactly like eating the flesh of your son, or your father, or your daughter, or yourself. And it is good and right that it should be so. It is good and right, because that cruel, harsh, apparently "evil" truth is part of a much greater pattern - a pattern which is at its root an expression of love/virtue/excellence/beauty. Death Metal Black Metal is right - nature is horror and light.... and even putting it this way is slightly erroneous at the highest level, as it implies that there is some distinction between the two at all.
Most authentic religions throughout the world express, either explicitly or in a playful, roundabout way, the understanding that there is really no sin except for ignorance. No particular action has any inherent value, no matter how cruel or benevolent. The goodness or lack thereof of an act has everything to do with the inner reality of which it is an expression, and nothing to do with the exterior reality of morals and consequences. That which is authentically good/holy/virtuous is that which is an expression of understanding/love of reality. That which is sinful is that which is done in ignorance/reaction-to/contempt-for reality. Fully grasping this concept, and also grasping the essentially good/excellent/beautiful nature of the world of natural phenomenon, with all of its blood and guts and terror and glory, one should be able to understand that the truly sinful attitude here is that which is expressed in the Ahimsa quote, and not that of the flesh-eater (at least not inherently).