That's why I asked the question, which I do mean literally: What private company in the world has ever invested that level of money on something not likely to pay off for decades?

If you, or anyone, can come up with an example of a company actually doing that, not just saying they want to, then I'd definitely reconsider.

I'm guessing that you're talking about Planetary Resources with the asteroid mining thing? I didn't see much about hard numbers from them, but I'm doubtful that they will ever spend tens of billions of dollars before getting a penny in revenue.

I can believe that private companies are good at making longer-term investment in technology that directly benefits a profitable line of business that they're in. Stuff like Intel doing research towards smaller component sizes on ICs. But who's going to invest long-term in fusion power? There's no company with a revenue stream related to it that I know of. The costs will probably break a hundred billions dollars before anybody gets plants on the grid that actually generate any revenue at all. I'm just not seeing it. If it were a realistic solution, why isn't it already happening?