If you provide numbers, we can compare this massive harm with some other types of massive harms.

As for tiny amount of good - reclaiming control over storage of value from The Man is such a tremendous achievement that will help us fight tyranny everywhere. Bitcoin donations was the only type of funding russian government failed to stop when it started to clamp down the opposition. For me, this capability trumps your concerns about environment and crime any day.

I see arguments of this form everywhere:

Law-abiding, tax-paying, responsible citizens use Tool X for legitimate purposes. Criminals also use Tool X for crimes. Therefore, we should ban Tool X.

Tool X = {cryptocurrency, encryption, firearms, drugs, etc.}

Tools that have legitimate uses should not be prohibited to law-abiding citizens.

Absolutely prosecute people who use the tool to hurt other people, but don't prohibit the tools that both bad people and good people use.