Not so much with excerpting, but cutting, yes.
There are a few schools of thought with cutting material from theatrical performances. The first is that cutting out extremely old references (such as in Shakespeare, or Moliere) will help the play and prevent temporarily confusing the audience. Another believes that the playwright had an original intent and all words should be honored exactly as written. A third way of thinking is that for productions featuring minors (such as a high school production), it is okay to cut out stronger or explicit language or content as long as it does not interfere too much with the flow of the storyline or create a different representation of the character the audience is experiencing.
If you should ever seen the full, uncut version of Hamlet, you may be in the theatre for about four hours. I was in a staged version of 'All's Well That Ends Well,' and various cuts were made. For example, in a speech Parolles makes about virginity, the line "Virginity, like an old courtier, wears her cap out of fashion, richly suited, but unsuitable, just like the brooch and the toothpick, which wear not now" was cut due to the comment being related to fashion during Shakespeare's time. The director wanted audiences to believe the play could be transpiring at any time, and also be able to follow the story cohesively.
As far as ethical considerations? Well, there are some who believe no stage directions should be followed--the words in italics and sometimes parentheses before, during, or sometimes in-between lines. Some believe this was the stage manager making notes during the original run of the piece, and should be ignored (even blacked-out with marker) so that the chosen actor can pursue his or her throughline independent of 'how another actor did it.' Others believe the playwright themself put this direction in for a reason, and so actors must use this direction as clues to the objectives and wants of their assigned role, and use a chosen technique to elicit what they believe will portray or emanate what is italicized.
So yes, some believe that ethically, playwrights had an original intent and will not cut a single thing, no matter what the cost. Others who wish to take time and audience consideration will sometimes make cuts.
