Jonathan Ball believes that in my first paragraph I explicitly 
acknowledge that I am assuming the conclusion that I am trying to 
prove, and hence he feels no obligation actually to engage with the
argument.

This view of his is incorrect. In my first paragraph, I am attempting
to set the argument in the context of the existing literature. I am
telling my audience that among the philosophers who advocate radical
reform in our treatment of nonhuman animals, different thinkers hold
different views and subscribe to different frameworks, but that they
would all accept the argument I present in my talk as sound. Thus, in
my talk I am not introducing them to all the different ethical 
frameworks and the differences between them, but presenting one 
argument which all of these thinkers would accept as sound. Thus, I
am simply situating this argument within the broader debate. I am in
no way implying that the argument would only convince those who
already accept the conclusion, and I find it difficult to see why
anyone would make such an interpretation. I think that the argument
I present should give pause for thought to any reasonable person. Maybe
Ball could make some effort actually to engage with it.