Not to be confused with gambling, where your tokens do not represent your or anyone's ownership of any tangible asset.
Why is this the line between investing and gambling? I might own $1 billion of equities on swap. This is just a bookkeeping entry that my dealer made up to take my money. I don't see how not owning the physical stock suddenly makes it gambling.
The Japanese FX broker, on the other hand, has the odds so firmly stacked in their favour that they have no need to actually do any FX trading (though I expect that they do some). If the margin is high enough, the statistical fluctuations don't matter that much. That's the difference between a brokerage and a bucket shop.
My point is more about ownership (legal vs beneficial). See: https://www.sec.gov/comments/4-537/4537-25.pdf
It would be interesting to seeing a similar legal analysis of ownership applied to bitcoin exchanges (and wallets, bitcoin clients vs mobile).
Which is a complicated way of saying that the share that I think I own actually exists in the world, through an admittedly complicated web of commercial relationships maintained by professionals at regulated financial institutions. It is not simply a bookkeeping entry that my broker made up to take my $2. If I sell it, I will likely end up selling it to an internalizer who pays eTrade for the privilege (Citadel?), rather than a counterparty on a lit exchange, but it still exists. It votes in BoA matters. It receives dividends. It seemlessly transfers when I migrate between brokerages, which I have done twice since buying this share. If I wanted to pay an irrational amount of money to win internet points, I could probably even gain physical custody of an actual share certificate.
If you want to nerdsnipe further about the difference between bucket shops, Bitcoin exchanges, and financial institutions, I am happy to go into this topic in arbitrary depth.