the definition Art is tied to time and culture. How art was defined or seen in the Renaissance is different from the surrealist and from the minimalist and contemporary art. So through time, the definition of art is rapidly changing.
Through the discussion, nobody is wrong, but the definitions are coming from different timelines and most won't work for contemporary art (the art of this time).
art in the contemporary is 'what is not art'; yes!
the boundaries of art have been pushed to the point of the art we know vanishing.
so the beauty might not count, the medium has changed, the skill might not be even relevant.
And these make Marcel Duchamp's work art, same to Chris Burden.