Why is Twain using the events involving the king and the duke to blur the lines between the comic and the dramatic?

The Duke and King are con-men. Initially huck finds them entertaining. Their banter is ridiculous, and their con-jobs seem innocent enough. Their enactment of Romeo and Juliet on the raft is quite comical. Still, there is an undercurrent of nastiness to them. Huck discovers that they have no concern for anyone else (they try to get Jim captured), and that there is some type of hurtful fall-out wherever they go. After their "hijinks" there is little that is funny about who they are and what they do.