GeorgW said:
Images are different. There are a lot of image macros out there that have been created to perfectly sum up thousands of different people's opinions. Why bother to say something in a way made for the exact purpose of being unoriginal? There's nothing wrong with using images to enhance your opinion, but to let them completely embody them is just lazy and discourages discussion.
You said yourself that it is what is said that is judged, not how. Why does the medium in use change that? An image can often convey whole concepts, innuendo and subtext in a far more efficient and stronger manner than words can manage. If the concept you are trying to convey is covered by the image, why does it need a tacked on explanation? Oftentimes that actually reduces the impact of the point being made.
Also, with regard to unoriginality: Context is king. Depending on the context, there could be a number of different meanings for the same image, that's one of the strengths of a visual medium. It all comes down to the discussion and how it relates. Plus, unoriginality is not inherently a bad thing. Innovation is great, but sometimes "it's always been done that way" is actually for a reason.
Finally, I would disagree that images discourage discussion. Discussion is the sharing of ideas and concepts to improve, hone or otherwise shift both your own and those of your listeners. Those same ideas and concepts can be shared just as easily, sometimes moreso, by an image than any number of words. Any further argument on this point is down to semantics, so I'll leave it alone.
I'd leave off with a pithy/witty image summarizing most of this post, but I can't access my repository of images from work

.