Thank you for sharing your thoughts about how to proceed. I might
include a discussion of R. M. Hare's views, in particular his essay
"Why I am Only a Demi-Vegetarian". That might do something by way of
addressing your points. Your question about whether speciesism can be
"justified" in nonhuman animals strikes me as ill-posed. There will
probably be some discussion of this point in the project as well.

I do not currently have any preconceptions about what conclusion I
will arrive at.

It is probably best to let me finish my thesis and write up the first
chapter before we discuss the matter further.