Very funny quote! However I would have to say that I do agree with it. Like a number of Shakespeare's comedies, there is often a sharp taste in the tongue alongside the sweetness. In fact, you might want to think about the genre of Comedy and Tragedy and how often his plays seem to lie in the middle ground between both of these categories. Merchant of Venice for example, seems more tragic in parts than comic, and equally Othello has a number of ingredients for a hilarious comedy - over-jealous husband etc.
However, in Twelfth Night, the major "sharp taste" comes from the character of Malvolio and his treatment at the hands of Sir Toby Belch and his cohort. Although his "punishment" for his arrogance and self-love can seem to be fitting and is something that the audience can enjoy and laugh at, it does seem to have been pushed too far - the punishment does not fit the crime. If it had stopped at the ridiculous yellow stocking event that would have been punishment enough, but to lock Malvolio up and to make him doubt his own sanity smacks of sadism, and does not "fit" easily into the standard happy ending of this comedy.
However, through his punishment Malvolio is a character who we come to respect and admire. He has dignity in the way he stubbornly clings to his sanity, despite being goaded by Feste. It appears that he, the character who represents order and Puritanism, must be locked away to enable the other characters to enjoy the riotous disorder of the Twelfth Night festival. Malvolio remains true to himself, and although he receives no recompense at the end of the play (he doesn't even receive a proper apology) we respect him all the more for that. He exits out of darkness into a celebration where he is excluded, and he stalks out, presenting a dischordant jarr to the festivities with his final words: "I'll be revenged on the whole pack of you!".