Humans are creatures with feelings as well. People believe exposure to certain messages (like advertising) influences people, whether consciously or no. Reminding of the downsides certainly can have an effect, even if that knowledge is already known.
> Reminding of the downsides certainly can have an effect
Like in the joke: A smoker asks for a pack of cigarettes and receives a pack which says that smoking causes impotence. He returns the pack to the cashier and says he doesn't want the pack with impotence, he prefers the pack with lung cancer instead.