Hmm, it’s true that cold fusion would need some kind of physics breakthrough, although I think it might be going too far to call it junk science. To be entirely fair energy positive hot fusion also requires some kind of physics breakthrough though, although potentially a far less extreme one.

The Sun works because of its mass which generates the necessary temperature and pressures to trigger the fusion. Replicating those pressures and temperatures here though is incredibly energy intensive. In theory, on paper the energy released by the fusion reaction should exceed those energy requirements, but when you factor in that doing so requires exceedingly rare and expensive to create fuel most if not all of that energy surplus vanishes. Nobody has been able to prove that they can get more energy out of the reaction than the energy cost of creating the fuel and triggering the reaction, so until that happens hot fusion is far from proved either. There’s a few research projects that look promising, but it’s far from guaranteed that they’ll pan out.