Except that if you can generate enough power for it (which is entirely conceivable in a sci-fi setting), then any directed energy weapon that can fire a sustained beam is going to be able to massively out-perform any weapon that fires a physical projectile with regards to damage output. Add in the fact that it requires only energy as ammunition and the "projectile" travels at or near the speed of light, and you have a gun that can't be evaded and isn't affected by gravity or atmospheric conditions at long ranges, and there's nothing stopping you from making the beam invisible and silent. Perfect sniper weapon.

Star Wars just did it wrong.