In some cultures eating horse meat is normal, in others vegetarianism is the honourable goal. Have you ever asked yourself why you eat or why you don't eat some animals? It is typically a product of the culture we grew up in, rarely the product of an intentional thought process.
Would you eat another human? What about another ape? An elephant? A monkey? A cat? A rabbit? A cow? Where do you draw the line?
I once decided that the "mirror test"[1] was my litmus test for eating or not an animal. But then as I looked more into it I realised that that test isn't as straight forward as I thought, lots of false positive, methodology issues (eg: some animal start passing the test after being exposed to mirrors for a long time). And the final blow was that most humans under 6 months fail the test and I decided not to use this test rather than starting to eat human infants.