Governments have a record of being very good at collecting and spending money on extraordinarily expensive projects, but are very bad at making things cheaper and more affordable.
GP's point was "tax the fuel". It doesn't matter what the govt does with the revenue - for my pov, current taxes on fuel don't compensate the huge externalities and side costs of it: Half the police is dedicated to roads, half the city space is roads and parkings, 75% military is attacking petrol producers, we have cancers and asthma, and the global warming will cost us natural disasters and economical inequalities. If we integrated that cost to the gallon of petrol, which would only be fair, the gallon would be 5x or 10x more expensive, and we'd watch the economy innovate, as GP said.
First we can immediately lower the income tax. Second, the current price is actually a loan on all of the victims. Third, the tax can progressively increase along the months, so industries can plan exactly when their renewable products will be market-competitive.
I don't think 'affordability' is the relevant metric here.
I'm talking about EROEI - the viability of doing it at all.
Private enterprise can play the capitalism game and make it cheaper. But it won't invent breakeven fusion to begin with. The risk appetite just isn't there at that level of investment.
I think the way to look at it would be to imagine that you are optimizing some utility function which incorporates some mean and some variance.
The risk of going for a clean energy project is massive. It can fail completely, it could work but not return much profit, there are lots of ways it can go wrong.
However - the problem here is that the 'do nothing' state is not static utility. Do nothing results in everything going to shit, with very little variance.
Our capitalist systems aren't really set up to deal with that, it's a tragedy of the commons. That's why you need things like taxes on oil - to force the utility function to accommodate bad things.