Usually, the word "addiction" has negative connotations. When something is addicting, it implies that we're powerless over it. It's also frequently true that the things we're addicted to are bad for us. If, however, the objects of our addiction have no ill-effects is it still a problem to crave them?
Cigarette companies have faced decades of trouble for trying to find a way to make their dangerous product more addicting. Soda companies are known for adding caffeine gratuitously to get children hooked. Even McDonald's has been said to use copious amounts of sugar in their french fry recipe to keep people coming back for more. Is this practice ethical? Is there anything wrong with adding ingredients just to cause an addiction to a product? What if the product was water? If there was a completely benign substance that you could add to water that would keep people constantly drinking it, would that be ethical? Is it ever okay to knowingly weaken someone's decision making abilities?