Rajan, it is a valid question.
How we rationalize this is by 'sentience'. Not 'sentence' like stringing a bunch of words together; but sentience as in the ability of a living thing to feel or be conscious.
We could make an argument that vegetation might be sentient, but it's a stretch.
In ancient times, humans had to eat whatever they could pick, kill or scavenge.
The modern world has the skils and ability of eliminate killing animals and using them for food. But it is not going to happen.
I was told by a poultry farmer (I know that this was your business) that the chickens he raises go from egg to Kentucky Fried Chicken in the short span of about eight weeks. Based on your experience, is this so?