When Luke Skywalker loses his right hand, he chooses to get a robotic hand rather than learn to swing a lightsaber left-handed. He's lucky to live in a universe where a prosthesis can perfectly replace a human hand. After Jaime Lannister suffers a similar loss in A Song of Ice and Fire, the Kingslayer struggles for years to learn how to fight with his left. In all the other worlds of our fiction, the right hand remains the default choice to swing a sword, whether it's made of iron, laser, or dragon-steel. Hand dominance is such an integral part of human life, it's a rare writer who creates an alternate world full of humans or as-good-as-humans who use both hands equally. It's good that nobody writes those worlds, because humankind without handedness would be a completely different creature.