I think that it is not a pure sum zero game. It has a input, the money from illegal activities (drugs, black money, illegal prostitution...) which has less value as input that as output.
So put your life savings into shorting bitcoin. It's a sure thing right?
“The market can remain irrational longer than you can remain solvent.”
Arguments against Bitcoin and other cryptocurrencies fall apart when you realize people are using it for more than frivolous speculation, such as to escape extreme currency controls from their totalitarian governments. And no, asking said governments nicely to please not screw us as hard daddy doesn't work, because the new tyrant who ends up in power after overthrowing the previous government will end up just as bad.