Considering the fact the he's probably never even heard of the term lightsaber before, and probably had his uncle intentionally keep him from learning about the Jedi. Its not like its a blaster or something that is uber common. Its like handing a pistol to someone who has lived their life outside tech. He's not going to know what the hell it is. So luke gets some slack.
He doesn't get 'slack', that proves he's even more of a moron. I mean, come on, even if he did get slack for that, his other idiocies for surpass all. If he didn't have friends with half a brain to save him from every thing, or just plain dumb luck on his side, he might have lived through an hour of the first movie, (If only).