Why do research on something at all, if it could be misused? What if we invent a new sabre blade that's made out of light and can cut through almost anything, i

Why do research on something at all, if it could be misused? What if we invent a new sabre blade that's made out of light and can cut through almost anything, including people? Should we not invent it? Would we only give it to a Jedi, who could be trained to never do bad things with it? Why are these researchers doing research on this? Seriously, why? Why do research on something and then not release the model over gasp ethical concerns -- if they had ethical concerns, why did they pursue this avenue of research in the first place? Why advance the state of the art if it's wrong to do so? Not releasing the model for "ethical" concerns is a cop-out. There's probably another reason; what is that reason?