"i can't understand why people are frightened of new ideas. i'm frightened of the old ones."

the point of avant-garde art is almost always to challenge the idea of what it is (eg. is this a sculpture? is this a play? is this a song?). in other words, the point of it is to get people to ask, "is this art?"
so, people always doubt that avant-garde art is, in fact, art. but i think that the question is more, "is mainstream art art?" because, like, those paintings from the 18th century of lords and ladies who have paid the artist to make them look good, they're not really art. they're more a service. isn't the point of art to expand the viewer's consciousness?
therefore, if art follows all of the popular conventions of its medium of the day, but its only purpose is to entertain or to gain popularity for the artist, is it really art?