Most good scifi doesn't try to break away from reality, but theorize about technologies that could be possible in the future. Obviously we don't know what future science will bring so it's impossible to be 'realistic'. But it seems reasonable enough to assume that though current lasers are pretty shit, some kind of photon stream could be weaponized effectively eventually. It's naturally suited because photons carry energy in straight lines at maximum speed which is pretty much exactly what you want from a gun.
