The economic and monetary risks of deflationary coins are potentially much greater than the environmental risks imo (Even Douglas Adams tried to warn us: https://benoitessiambre.com/specter.html ).

You don't necessarily need to ban the coins to fix this aspect however, just make sure they don't get integrated in the financial system too much. They're basically digital gold. Gold was ok until central banks tried to anchor to it which caused the Great Depression and maybe even WWII.