Where does this idea that fusion == infinite energy come from? Nothing could be further from the truth, all fusion power plant designs have a very fixed amount of power they can generate (limited by the size of the reactor), and the costs to build and maintain one are gigantic, in ways that are unlikely to go down in the next century or so. Scaling them up (building bigger reactors) is extremely hard because of fundamental geometric reasons, and scaling horizontally (many many power plants) is hard because they require teams of experts to run and monitor.

And pretty much the whole plant, with all the expensive magnets, supports, and reactor chamber, has a lifespan of maybe 10-15 years before the constant neutron bombardment makes the materials too brittle to keep supporting their weight. You then need robots to come in and dismantle the highly radioactive components and store them securely for a few 1-200 years while they cool off.

Sure, it's nice that fusion requires relatively little fuel (though even that is not that great, since it requires an extremely rare substance, tritium), but that doesn't mean it's in any way going to scale up infinitely, or even a lot, or even as much as nuclear fission.