This is a really interesting point - I think the question will really come down to how well campaigns / businesses can measure the impact of their marketing. If your messages/posts aren't driving donations or purchases (or hurt the long term usefulness of the person you're marketing to), then you won't run them.

The problem is that today most marketing is blind - completely unlinkedin from the impact it causes. I'm counting on technology / big data / analytics to change that.