Well, that’s sort of strawmanning my argument isn’t it?
I started with the disclosure that we all believe consciousness exists in some form. That alone separates my argument from your example: consciousness exists, Florgleblorp doesn’t. If you alternatively want to argue that consciousness doesn’t exist, that’s another conversation I’m willing to have.
Consciousness isn't some arbitrary word we've invented and subsequently gone searching for a referent. We already have the phenomenon we're attempting to explain: subjective experience. What we lack is a sufficiently established understanding of what constitutes it, how it arises, and how to reliably identify it in other systems.
That's how scientific investigation frequently works. We recognize phenomena before we fully understand their mechanisms or develop reliable criteria for identifying them.
Of course we need provisional definitions to investigate anything. But an operational definition isn't automatically an accurate characterization of the underlying phenomenon. That's something we have to establish through evidence.
Otherwise, we're just choosing which properties count as consciousness, constructing tests around those properties, and treating the results as validation of our original assumptions. That approach, which is what I’m interpreting your suggestion to mean, is not reliable. In fact, it’s dangerous.