F I R S T L Y: Though this poster may seem humorous by nature, it was not intended as a joke because not only are rape jokes disgusting but I am as serious about my love for all things Harry Potter as I am about my stance on social and sexual politics. Rape is an unpleasant but extremely relevant topic in our times and combatting its culture is as important in the magical world as in the muggle world, so I hope that every child will be taught that using a love potion that comes in a can with a percentage on it is just as bad.
Might I add that Jo 100% feels the same way as the OP. Just look at all the negative effects love potions have. Jo has said that a child conceived under the influence of a love potion will be unable to feel love (EX: Voldemort). Clearly those consequences are a message to readers saying that rape is under no circumstances okay.