The fundamental reasoning behind Laertes' objections to Ophelia's relationship with Hamlet mainly lies in true care and concern for his sister while Polonius' objections lie mainly in his concern for his image and his power. Laertes' advice can be seen as a true desire for the well being of his younger sister.
Polonius sternly echoes Laertes' advice and forbids Ophelia to associate with Hamlet anymore. He tells her that Hamlet has deceived her in swearing his love and that she should see through his false vows and rebuff his affections. Ophelia pledges to obey.
Polonius always thinks Hamlet is crazy!
Ophelia indicates that she will remember Laertes's advice when she says, “I shall the effect of this good lesson keep”
B, because if you don't have anything to back up the argument then you will not have a steady argument making the "debate" on your side turn into an opinion.
