I'm sure there are many answers to this question, but here's mine.
Any rhetorical practice is a composition. Something is composed: a message, a sentence, a thought, sounds, gestures, data, etc. To establish a theory of composition is to establish an ontology, a theory of being and becoming. Perhaps in my field, that ontology is often implied and unexamined, a humanist-Enlightenment philosophy, or if not, then it takes some postmodern form via cultural studies, Foucault, and so on. So the short answer is that one pursues a speculative rhetoric because the extant ontologies of rhetoric are found wanting. Or one might even say that they devalue ontology, insisting that questions of composition, agency, community and such are discursive, epistemological questions, questions of ideology and representation.
However, I obviously see this differently. Not only would I say that a theory of written composition or communication or symbolic behavior rests upon a general ontological theory of composition. I also view questions of rhetoric as intertwined with questions of cognition, agency, and affect.
- How do we record, retrieve, and process information?
- How do we account for the activities produced by rhetorical relations?
- How do we describe our ability to be affected and affect others via rhetorical practices?
The way I've phrased those questions leaves open the larger question of how far to extend rhetorical relations, which is another arena a speculative rhetoric enables (i.e. how does one draw the boundary between rhetorical and non-rhetorical relations and practices?).
I came to speculative rhetoric via Deleuze, DeLanda, Massumi, and Latour, particularly theories of assemblage and actor-networks. I came to this point organically from what I believe is an obvious realization for anyone who has ever played music (or perhaps composed in any non-textual medium): composition cannot come simply from "inside." Somehow, culturally, we have allowed ourselves to overlook the role of writing technologies and communities when we think of written composition, but anyone who has ever cursed out their multi-track recording deck or guitar that won't stay in tune or spent an afternoon trying to figure out why you keep getting feedback or stapling foam to a wall understands that composition isn't inside. So I started there, 20 years ago, and without even giving it much thought, I brought that perspective to graduate school. So I didn't really experience cognitive dissonance in thinking about networked composition or distributed cognition.
Of course the things you are hooked into will shape what you compose.
It gets more complicated from there as one tries to develop a theory for how that works, but for the rhetorician the theory is only part of the issue. In some ways the more interesting question is how does the theory open new possibilities for composing? And for the academic rhetorician, the question might be how can I take this scholarly work into the context of my obligations and commitments to teach? And best of all, for the rhetorician who has struggled with the hylomorphic relation between conventional theory and practice, a speculative rhetoric can never be prescriptive. It is simultaneously more and less than a methodology. It gives us a new way to think about the knowledge we produce, one that is both less certain in epistemological terms but also more connected to the world.