astromech said:
Perhaps Luke's newly built lightsaber had a stun setting so he didn't have to kill - after all, that would lead to the Dark Side.... :p

Silly astromech. Everybody knows that only killing major characters leads to the dark side. You can kill as many extras as you want. But you're right. Luke must not have done much of the killing. He just gently nudged them (with his lightsaber) off the skiff into a slow, painful death at the hands of the sarlaac. Totally different than actually killing them. ^_~