That is kinda the main point of a carbon tax... it is to make carbon usage LESS efficient, since you have to pay an extra tax in addition to the cost of the energy itself. Ideally, the money gained from the carbon tax is then redistributed to everyone equally, and that money can then be used for whatever you want.
i dont think that's a good idea - the redistribution does not decrease carbon.
I think the correct carbon tax is the amount of money it takes to fully remove the carbon emitted (at current tech levels). This pot of money is then used to actually remove carbon.
This is not true. Often, renewables aren't available to some locations but abundantly available in others. Other times, some people buy electricity from renewable providers and others don't.
With 50-75% of Bitcoin mining being renewable, one thing is clear - it's helped the adoption of renewables and made them cheaper.
Miners are chasing profit margin so they'll use whatever's cheapest. If that's renewable where some of them are, so be it. And if everyone else start reducing use of coal and that becomes cheap, miners who exploits that to derive higher profit margin will grow faster I imagine.
I would attribute growth and economies of scale that renewables have achieved to renewable proponents, industries, government subsidies and loan prorams. Crypto miners are energy consumers and some of them use renewable energy. But how do we go from there to miners being some kind of force for good in this context?
Any excess capacity spent on crypto currency is waste. It could go to scientific computing projects, it could simply not be used. The chips for the equipment (we are in a global chip shortage) could go to something that actually contributes to the real economy.
We just need to increase carbon taxes at the same rate that renewables become affordable.
We have about a few thousand pressing issues that spur us on to push for renewables as it is, we don't need to waste energy on purpose.
Crypto mining is one of those issues, we don't have a choice. Your argument reduces to "if we had no issues pushing us, we would have enough issues pushing us" which is a contradiction.
This is an example of Jevon's paradox, namely that increases in efficiency or quality are offset by increases in demand. It's one of the reasons why we have globally barely made a dent when it comes to the increase of renewables as a total share of energy consumed despite the fact that the capacity has increased pretty much exponentially.
This is made even worse by the fact that green infrastructure itself necessarily often consumes non-green sources, in particular during construction.