still looks cool, though the guard isn't really functional as if a light-saber touched it, it would be cut off.
The cross guard doesn't
need to be functional, does it? Why can't it just be decoration? An expression of the personality of the wielder? Designed just to be menacing and intimidating looking? Have you seen half of the designs of fantasy Swords out there? They're often just as bad.
Put a ridiculous cross guard on a fantasy sword, and no one bats an eye. Put a cross guard on a Lightsaber, and everyone loses their minds.
((Posting from my iPad, too lazy to make the meme for that....))
In all seriousness though, the cross guards on most bladed weapons are usually just as much, if not more, to protect your hands from sliding down your own blade, as they are to be used defensively against attackers. Particularly since in medieval combat you'd be wearing thick leather gloves that may slip on the grip of your weapon when performing certain attacks, especially if you get any sort of mud or blood on your hands in a fight. This can be even worse for the less privileged soldiers who may not have had the luxury of gloves, and didn't want to risk slicing their own fingers off on accident when stabbing someone in the chest.