What was the rationale for adding yet more complexity for us filling taxes...
[1] If you're doing that, you should, like, stop. I'm not a lawyer and this is not tax advice, but you should probably stop.
I’m only sort of joking, the IRS has historically scrutinized attorneys more than other professions.
Again, this does not change personal taxes.
Now, folks are on the hook for self-reporting. Previously, the thresholds were $20,000 and 200 transactions, which were maybe too lenient. Had lawmakers just halved the threshold to $10,000, I don't think most people would care. The $600 is too low, e.g. guitars easily fetch a grand, and Leica M bodies are easily over that.
Also, what are Nancy Pelosi's stock gains compared to any folks that might have been not reporting their illicit <$20k income?
This is basically the separation that sole proprietorships have to go through. Stuff that is exclusively used for your business is deductible, anything for personal use isn't.
I think you're working from a different set of assumptions than GP. They were specifically contending that exclusive expenses could not be deducted, even if the overall net value of transactions is negative (because it's not a business, but just a partial recovery of hobby expenditures.)