In effect, threads like these are sorta unanswerable. If energy suddenly becomes abundant, cheap, and non-polluting, then it likely means that either their has been a profound and era-changing breakthrough in technology, or we are talking about a fantasy scenario. In either case, it’s difficult to say what exactly the effects would be.
This really might go into a similar but alternate debate - “If some source of cheap, abundant, non-polluting energy becomes available, what are the barriers to using it?” Legally speaking, let’s say that a “Mr Fusion” is invented by a small company in Scranton, PA, and they hold so many patents on it that it is absolutely impossible for anyone else to legally produce one without patent infringement. And let’s say that this company, based on advance/actual sales, has the lawyers required to put weight behind their patent defences.
What happens then?
Does the Government “sieze” the technology, keeping it for itself, out of “national defence” concerns? Or out of “security against terrorists”? And when they seize it, do they keep it for themselves under a “national electric company” (and I’m not talking TVA), or do they make it public domain?
Do companies just willingly violate the patent, making Mr Fusions themselves? Do people, assuming it is possible, start a grassroots Napster-like rebellion to make garage Mr Fusions? Do we start hearing on the news every night about “energy pirates illegally downloading instructions to make Mr Fusions”? Jesus, it could happen.
What does the rest of the World do? In the non-public domain scenario, it could be sold for extortionist prices to other countries. Let’s say that the cost is $10 trillion - China basically says “kiss my ass” when it comes to intellectual property rights - can you imagine they would pass up stealing Mr Fusion for its 1.2 billion or so people? What about India?
Lots of issues here.