I have various positions on an array of philosophical issues, many of which are interrelated, and with variable levels of confidence. With any luck, I can form a generally cohesive philosophical framework that makes sense of many of my beliefs. I am quite doubtful, however, that I'll ever get many people to agree with the entirety of my philosophical beliefs.
When I try to advocate for a particular ethical view, then, I'm going to try to leave out anything else that I think grounds it. For example, if I'm going to try and convince someone that animals have rights, I'm not likely going to try and persuade them to share my views on personal identity. Animal rights are quite controversial, and so are my views on personal identity, so if I want to convince you on animal rights, it's best to leave out as many controversial premises as feasible. I will however, argue against utilitarian conceptions of duties to animals, because I think these exclude a proper understanding of animal rights. But for the most part, I don't need you to accept many of my other controversial ethical views if I want to convince you of animal rights.
This relates nicely to my discussion of speciesism and the qualities that individuals have by virtue of which they have moral rights. Now, in a broad reaching moral theory, there's a lot to say about what how certain qualities demand recognition of certain rights, and what it is about our own nature that makes it rational to respond to the moral features of others. These are interesting questions, and I hope to write about them here! But they're complex, and controversial. So the best way to get you to see, for example, that high intelligence is not a necessary criteria for moral consideration is to make you think about individuals with very low intelligence, whom you, in fact, judge to be worthy of moral consideration. It's a much better way to convince you than trying to argue about reflective endorsement, or how your prudential reasons are analogous to altruistic reasons, etc.
It's also better to argue this way because it puts more pressure on my own views. If obligations to animals could only be understood as plausible under one obscure moral framework, that should give me less confidence in my beliefs about such obligations. But since this is not the case, and since I think obligations to animals can be defended in a variety of ways, by appealing to many commonly-held intuitions, I can feel much more confident in my views on this matter. And hopefully, with any luck, I can thus be more convincing to others.