Very nicely put. While I agree on almost all accounts, I think it's worth noting that while market forces are in general efficient allocations of capital, it may be possible to identify particular areas of research or technology that the market, for some reason or another, in not incentivized to pursue. The best historical example of this is the Manhattan project. Sure, given enough time, defense entrepreneurs would eventually research and develop the same technology, and maybe at a much lower cost. However, the time-value of obtaining the bomb first could arguably justify the enormous expenditure (something around $20 billion in today's dollars). Now, like I said, this is mostly playing devil's advocate -- as an economics student, I tend to agree with you for most investments. However, I do think that out of all potential investments, green energy has the best case for justifying spending these billions of dollars.

Put another way, if we could pay $50 billion to develop a renewable, clean energy source right now, then it would probably be worth it -- even if it would take Elon Musk only 10 years to do it and for $50 million.