We obviously draw distinctions between art (whether fine or folk) and design, but these are largely descriptive distinctions that have little bearing on what so

We obviously draw distinctions between art (whether fine or folk) and design, but these are largely descriptive distinctions that have little bearing on what someone else ought to make or not. The absence of a definition codifying the functions, constraints and responsibilities of art (or design) didn't stop people from creating it. It is ideal that an artist or designer know their intention (and perhaps audience), but our inability to force the work to fit in a descriptive box has relatively little bearing on whether the artist or designer knows their intent and audience. Likewise, intent is something we interpret in the work; if critics didn't interpret intent, I don't know how much they could possibly say that would be of interest. The frame of their interpretation is furthermore part of how we interpret and evaluate the critic's thoughts; not all critics of the same work have the same frames, nor do they all read the same intent. Even when an artist or critic states their intentions or frames explicitly: we aren't any more obligated to trust them than they are obliged to tell the truth (or, if you prefer, to fully understand their own intent.) Neither, for example, is likely to be forthcoming about biases in their work. I could give differing statements of intent every time I read the same poem to a different audience, all of which are fairly useless unless critically interpreted alongside the work of art.