Avant-Garde art (Man Ray - Dali - Naoto Hattori) are my favorite artists. One day I will own a set of Dali's Divine Comedy. Avant-garde music is tough to listen to. Performance art has to have a mind behind it, or else it is just bullshit.
Anyone can do anything they want and call it art. Art is subjective. I'm sure there's a few people who might possibly listen to Yoko as a artist. Though without the connection to Lennon and the Beatles, Yoko's voice would have never been released on the world. Which tells you just how much it's considered art. It's like Paul putting a mic on Linda and making sure it was turned off. That's love, with the realization "honey your voice sucks." Did you ever hear the live recordings with her in the background? It was mean for someone to release them.
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