This argument dates way back to 1917 when the 'Dada' Artist Marcel Duchamp signed a urinal and exhibited it as 'Water Fountain'. He called them his 'readymade' sculptures:
en.m.wikipedia.org
There have been other examples to this also. Carl Andre used to make 'sculptures' from piles of bricks:
'The Tate Gallery bought Carl Andre's Equivalent VIII in 1972 for £2,297 ($6,000). The purchase was controversial, with some critics questioning the value of modern art.'
So, what he's doing isn't actually anything new. Maybe it's a twist that someone ate his work at one point... I've seen installation pieces made up of tons of sweets though- if I remember rightly- I think anyone was allowed to eat a sweet there. So- his was far more elitest by comparison- he only granted another performance artist permission to eat the banana presumably.
But sure, it's crazy what some will consider art and pay for it. I've always slightly hated this type of stuff because I value skilled artistry. Somehow what I find even worse is so called 'Artists' who get other people to make their work! Yet, they get the credit for the idea. That's supposed to be the point if it though- conceptual art.
It's crazier still sometimes when you read what the piece is supposed to represent! I think they could have gone with a better interpretation personally. I think the 'piece' does much more on questioning things like originality, worth, intellectual property rights. Any one of us could gaffar tape a banana to a wall today yet- how much would we be paid for that?
It's obviously not the physical work that the person who bought it owns. I doubt they re-use the gaffa tape and, they have to replace the banana. So- it's the idea. The blueprint on how to create this 'masterpiece'. Is it even the artist themself who 'creates' the work each time? Likely not I imagine. So- they're not even paying the 'Artist' for their time. Just the permission to tape a banana to a gallery wall because their name obviously carries enough artistic merit.
What we all ought to do in protest is take our own bananas and rolls of gaffa tape along to the gallery to create our own versions. I expect that's breaking a law somewhere... Can you get in trouble for adding something to a gallery? It's making a statement though. That's what some Art is about at the end of the day.