The only ones legally questionable are the use of darknet markets and offshore banking (which isn't illegal, but maybe should be).

While it's true that other solutions may improve, and I think they might be forced to, it's difficult to imagine middlemen surviving when the fee they can extract goes to zero. It's also difficult to imagine another system providing irreversible transactions as quickly as cryptos do.

And I don't think any of the benefits go away after crypto goes mainstream.