Why is what other people do with their money a problem for you?
I think NFTs are stupid, but I don't think they're "a problem".
People spend lots of money on stuff I find stupid. I would never buy a Gucci handbag, they have about as much value as an NFT. But if someone else wants to, it doesn't hurt me, so, so what?
Because it added fragility to the economy, just like people over paying for mortgage backed securities in 2008. If it was a few foolish individuals that would be different, but reckless speculation has been actively encouraged by the Fed across the whole economy, NFTs are just one example.
