A long time vegetarian once told me she could never eat anything with a face.
For me, the act of eating meat, particularly anything bone-in, began to feel more like performing an autopsy than enjoying a meal (maybe the dissection bench at uni is to blame). A lump of muscle on my plate or the leg of some unfortunate chicken are unappealing body parts.
I suspect this ick factor was compounded by the horrific discovery that I was fed tongue and brains as a blissfully unaware child. In fairness to my mother, tongue is actually delicious when you have no idea what it really is and it was just this year that mum dropped the bombshell that my baby food was laced with brains.
More importantly though, I have a general feeling of unease around many farming practices. We are not fully informed of just how the animals offered up for my consumption lived and died. The reality of the terms "free farmed" or "colony raised" don't live up to their expectations. Even free-range chickens usually undergo painful de-beaking, and the transport and slaughter processes for livestock leaves much room for improvement.
Each to their own, of course, and I'm certainly not an evangelical vegetarian. I do however find it a little perplexing when on the receiving end of some strange, and even borderline offensive comments from all knowing carnivores.