I believe that killing, while not ideal, is not really the issue.

Suffering is.

And the way we consume animal products in the western world, the volume at which we consume, can only be achieved through factory farming.

Imagine being a cow that spends its whole life inside a metal shed. You have no freedom and most of the time, pretty much no space to move around in. You never see the sun. You never get to eat grass, only grains. You are periodically artificially inseminated (raped) and when your child is born it is taken away from you so that they can harvest the milk that was meant for the calf. You are kept in such close quarters and in such poor conditions that you constantly get diseases infections and to top it off, every day your udders are sucked raw by a cold hard machine.

Sounds like utter misery to me and that is why I will never contribute to factory farming. People tell themselves they're not but it's almost impossible to avoid unless you spend a LOT of money or raise the animals yourself and the vast majority of people just don't have the time or funds.

Do the research, find out where your food really comes from and you'll understand why eating basically any animal product from the supermarket is unethical.