It's not. He-3 is supposed to be maybe one day used in fusion power, but we're talking about tons of this stuff. Not only scale is off, also He-3 burning requires much higher temperature than D-T fusion, and this is just around in next 20 years pinky promise
People who think that it's a big deal also take Ray Kurzweil seriously, it's scifi noise
In practical terms, when DHS wanted to get He-3 neutron sensors, they bought out entire global supply for multiple years, for an application where only grams are needed and it's not used up. It's made from decay of tritium currently and it'd be less energy intensive to make it the usual way
the most subtle taliban infiltrator on lesswrong:
e:
he'll fit in just fine