Its quite hard to define 'chair' too, if you want to define it absolutely precisely. But we can still talk about chairs.
consciousness: the state of being conscious
chair: a person who presides over a meeting or committee
That said, i don't think "chair" is scientifically defined, because nobody does science of chairs. Consciousness on the other hand appears to be the subject of both scientific and philosophical investigation, therefore a common definition is desirable. What usually happens is the discussion derails around which definition to use.
Anyway yes I am familiar with the difficulty in defining consciousness, but you seemed to be making the point that agreeing the definition should be done before any other discussion, whereas clearly some fruitful discussion is often possible even though the definition is fluid. Indeed the article in the OP is essentially trying to work out one aspect of the definition. I gather he has a book where he puts forward a definition of sorts.
I 've seen too many discussions using those "fluid" definitions to be running away from them. Fluidity is usually employed as a smokescreen tactic to derail any productive argumentation by constantly shifting the goalposts