Hamlet Names His Own Flaw?

Pay attention to a particular line in the monologue spoken by Hamlet at the very end of this scene:  "I am pigeon-livered and lack gall."  Those who believe Hamlet's flaw is inaction point to this line as Hamlet naming his own flaw, owning his own flaw, and yet being unable to correct his own flaw.  Ironically, Hamlet has just set an ingenious trap (worthy of a noble character of high intelligence) at asking the players to perform the play The Murder of Gonzago.  As a first-time reader, one may not know of the plot.  As readers, we find out later that the play is about the murder of a king in order to gain the queen.  Hamlet, knowing his uncle will be closely observing this play, has set a trap for Claudius in order to "prove" Claudius is the killer, as the ghost has named him to be.  After concocting this plan, however, Hamlet becomes disgusted with himself (for quite a few lines, actually).  It is then that he names his possible flaw of inaction.