After roughly going through the essay, I think the writer just partially answered the task. The task requires the discussions on both views, however, the writer did not address the second view, which is
others argue that humans must employ animals to satisfy their various needs, including uses for food and research.
.
Not but the least, if not protecting them, let us not be a part to destroy them.
It seems there is grammar problem in the last sentence. Maybe it would be better if you rephrase it as following:
Last but not least, if we are not in a role to protect the animals, we at least should not be a part to destroy them.