Earlier quoted context omitted.
Ancient people did not see animals are beings with feeling, they were seen as useful production machines. It's only in modern times that we have the luxury of taking the animal's feeling into account at all. I'm sure you would want even more consideration for the animals, but it's much better today than it was.
How do you know that "ancient people" never thought of animals as having feelings? Seems an extraordinarily broad claim given all the cultures and ages that encompass "ancient people"
I don't find it difficult to imagine my great-great-great-great-(fill in the appropriate number of greats here to qualify for ancient ancestors) grandmother butchering a pig and not really giving it a second thought at all, having grown up on a farm myself. Hell, my current grandma is probably much gentler and gives the pork a much better time than my ancient ancestors did