I don’t know about weaponizing anything, but I do know the only energy positive fusion reaction was done by making a little pellet of hydrogen, carefully aligning a room full of lasers, and then zapping it into helium. Each time they did it, someone had to walk into the chamber to put in the pellet, and they’d have to spend a few hours aligning the lasers again.

You get more energy out than you put in, but it just doesn’t scale.