After reading your essay, my primary question is: Who are you to decide what someone else’s purpose is? Who decided that the purpose of non-human animals is to provide food and clothing for humans? Was it God? (I’m an atheist.) Science? (There is no scientific evidence that humans require the consumption of animal flesh to survive.) Capitalism? (That didn’t create animal agriculture, but is a primary force behind maintaining it.)
You mention the comparisons to slavery. At one time, white people decided that the purpose of people with my skin color was to be slaves. (Some white people still believe this.) Women have also been treated — and continue to be treated in some cases— as the property of men. When questioned on these practices, those considering black people or women to be property might have written the same kind of essay that you have posted here, stating that these groups were serving their rightful purposes in life.
Fortunately, society has progressed to the point where most people realize that having a different appearance from someone else does not justify treating someone as property. The next evolution will come when humans extend that reasoning beyond skin color, genitalia, and other human physical characteristics to species.