You described two different things: a psychological effect first, and then a market. The elephant example isn't mere-exposure.
Also, I'm not an expert on this but do we see more sensless killing by kids playing violent video games? This is usually the counter example to the exposure argument and I haven't seen it properly argued against.
In the US there's also been an interesting rise in sexlessness and male virginity recently [0] which is a fun one to compare with exposure to pornography. There is evidence that real-world conditions have a lot more to do with real-world action than pictures on the internet.
Also, I'm not an expert on this but do we see more sensless killing by kids playing violent video games? This is usually the counter example to the exposure argument and I haven't seen it properly argued against.