If we are taught manipulation is wrong, we never learn how to use it and we are less able to defend against it, and it puts us at a disadvantage when we have to deal with a less scrupulous person who doesn't have a problem using it.
Instead if we are taught that manipulation is a tool, and like any tool can be used for good or evil depending on the tool user, maybe we would get less upset at the beer commercial with the twins in wet t-shirts, but also we would be less affected by it.