It becomes an argument if you agree with the premise that people should not be able to prohibit others from doing things based on a spurious moral assessment. On those grounds, all kinds of frivolous activities - including eating ice cream - could be prohibited.

If you don't agree with that premise, then your opinion is bad (and you should feel bad), but at least you're being consistent.

> But CO2 emissions have both individual and societal costs and both individual and societal impacts.

Yes, but the source of these emissions doesn't make a difference regarding the impact. To stay consistent, you would have to argue that the social benefit of ice cream is too large for it to be prohibited, while the social benefit of Bitcoin is too low for it to be allowed. That's a highly subjective assessment, to be made for each and every source of CO2.

> There are a bunch of complications to that, and we (the whole world) have not gotten all that far with that.

If we can't agree on a CO2 tax, then we can't agree on a ban (or tax) on Bitcoin mining either. The same countries that would refuse CO2 taxation would become a haven for Bitcoin mining.