Speculation is zero sum ignoring adding liquidity to the market in a positive sum game

Everything else is positive sum. Trading, moving money, storing wealth...

But it's not stable enough to be terribly useful for storing wealth or moving money, at least by the standards of normal legal assets. So most of the value must come from crime and speculation.

Same for most things. Guy grow potatoes sells some and uses the money to buy stuff. For every dollar he takes out of his potato ecosystem someone has to put one in. Just how these things are.

For miners it's positive sum. For people who buy cryptocurrency with government-issued currency it's zero sum. They don't show up with cash and go home with nothing. They get that amount of cryptocurrency. They only lose something if the value goes down. Which it might, or it might not.

You're using the term zero-sum incorrectly. Look up zero-sum game.