That seems like a lot of work to get deuterium and tritium on Earth. If mining them from the moon is really the cheapest option, I am even less optimistic about fusion.
It's a lot of work to set up the operation (any extraterrestrial endeavor is) but once there it should be possible to launch canisters of fusion fuel back to earth cheaply using some of that fuel for power, a railgun, and the fact that the Moon is tidally locked to the Earth.
Could easily be cheaper than sifting through huge quantities of seawater for the right isotopes.
