I think everyone is manipulative to a certain extent, never more so than in the way we present ourselves to others in order to garner their support/empathy/advocacy. Manipulation is not by definition harmful as such. Babies manipulate their parents from birth.

In addition, I've always considered myself fairly easy to manipulate, and even when I notice it, I usually won't mind it (whatever it is) unless:

a) It's something that's hurtful to me.
b) It's something that's hurtful to others.
c) It's being done by someone who has no respect, i.e. they're attempting to elicit an action, behaviour or response from me that they aren't capable of themselves.

The instances above are when it becomes abuse rather than socially acceptable human behaviour.