I'm a painter/illustrator. Lots of art, especially post-abstract expressionism, is definitely a joke.
What if the definition of art is applying some paint to a canvas?
In my experience, copyright and IP law have been leveled against me in employment contracts more than than they've ever helped me maintain a grip on my output. 'Intellectual strip mining' is a good way to put it. The definition of art hasn't protected what I do and changing it probably wouldn't affect that.
There is also a controversy with that piece by Duchamps; there is some evidence it was by Elsa von Freytag-Loringhoven.