I suppose in the sense that concentration of mining power makes a cryptocurrency vulnerable to 51% attacks or that concentration of mining power centralizes influence and cryptocurrency in a way philosophically antithetical to the principle of decentralized cryptocurrencies.

I suppose you could call them weapons of environmental destruction.

I suppose you could call everything produced by man weapons of environmental destruction, but that doesn't make it very useful.

You dilute the meaning of the word at that point. Weapons are specific tools that are used with intent to cause harm. If something happens to cause harm without intent, and you define it as a weapon, the word becomes useless.

You formulated it clearer and better than I did.