Giving a counterargument allows the essay/writing to contain more perspectives that strengthen the claims as more perspectives allow the reader/viewer to see an overall "picture" of the argument. Also, being able to "debunk" the counterargument as false or not strong will help in strengthening your own essay/argument.
Including only your side of the argument leaves the reader/viewer no perspective of the whole topic.
(if) the magician were to get leery warnings about how he can turn bad from using too much power, you would expect for it to (maybe) happen some point during the story.
"b. He is laughed at, ridiculed, and abused" is the best option as to how the beggar Odysseus treated by the suitors, since he later opens his arrows on them.