A lot of the 20th century's must pressing questions in art are left unanswered. Many of them were posed rhetorically. Can't art be this? Why can't it be that, too? What about these issues? these people? these theoretical positions?
One studies each of these propositions in their turn, and eventually one arrives at a position of being positively stymied. It's as though all those questions were primarily asked so as to prevent any answers from ever being positively, or even just tentatively, accepted.
It's as though so many of them are accepted as negative critiques that no positive proposition can be proposed after them. We accept that just about anything can be posed as conceptual art, but in so doing, we renounce anything, everything, not conceptual enough.
Not a good move.