You cannot change the past but you can start now and lay the foundation for the future.
Remember that everyone you see and every situation you find yourself in has come from inside of you; you have created your reality by how you have treated others in your past.
It is true that every being is enjoying life or suffering as a direct result of his or her own past actions. The animals in the factory farms may have been meat-eating human beings in a previous birth; we don't know, and it is not our place to judge.
Everyone is caught in the web of his or her own actions and is bound by past karmas (actions). Good and bad are relative terms. Every action takes one to the next place.