As an author, it is clear you need to restrain the speech. As a commenter, I have more freedom with this respect.
To come back to Darwin and the discussion, we must keep in mind that knowledge of that time is not today's knowledge. Something that may sound cruel and immoral today could have been "normal" hundreds of years ago (regardless whether we agree or disagree). This being said, even if there is no scientific proof (yet?) that animals are sentient, they may be (I guess this is clear and does not need to be proven). Therefore, we should behave as they are (better be sure than sorry).
PS: I am not afraid of long blogs as you can imagine ;)
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