Answer:
Laertes and Polonius are opposed to Hamlet's and Ophelia's relationship because they believe that Hamlet is just flirting with her and do not have intentions to marry her.
Step-by-step explanation:
In Act 1, Scene 3, of the play Hamlet, we can see Laertes and Polonius giving advice to Ophelia to reject Hamlet before he rejects her. They assert that Hamlet is of high rank than her, therefore, he will not choose her to be his wife. They remark that Hamlet does not have any intentions to marry her, all he is doing is flirting and trying to use her.
Though Laertes and Polonius know that Hamlet will be the future King yet they oppose their relationship because Hamlet's intention to be with Ophelia was not seen as a serious business to them.