Cryptocurrency is the biggest backwards step for the climate since CFCs.

Thats a huge misconception actually, the information you have is the amount of energy being used, but you don't have information on the source of the energy.

Would you be willing to accept or at least corroborate that cryptocurrency mining is one of the cleanest sectors and a boon for sustainability?

70-80% of that energy use is renewable energy or reducing pollution - specifically hydrocarbons. So existing energy is not being wasted or reallocated, and additional unclean energy is not being ramped up to facilitate mining, and previously wasted energy that was going into the atmosphere is now being used.

The educated discussion is to make sure it stays this way. As nation states are the only actors that could mine at a loss with inefficient ways.