Unrestricted social signaling games absolutely have runaway costs and zero net social benefits; if we're going to address those, we're right back to "charge for externalities", which was the solution anyway, and completely unspecific to Bitcoin.
Edit:
>But I agree with the general point - pricing in full externalities of energy use would go a long way towards fixing things, including Bitcoin's existence.
Why do you say that? it would just change the total equilibrium expenditure on mining, not render it pointless, since the blockchain just has too be too expensive to attack, and the same constraints would apply to attackers and miners.