When I first saw the movie as a kid, and saw Luke's black outfit ... force choking the gammorean guards and how arrogantly he threatened to kill Jabba, I was afraid he had already turned to the dark side. To me it didn't feel at all like he had any other plan than to eradicate Jabba and his gang.
Even nowadays I think the whole rescue scene depicts the corrupting influence of his new found powers (i.e. 'delusions of grandure').