In the efforts of clarity and in an act to 'show all my cards', I'm going to explain the two problems I had with the image. I know one to be subjective, and that policing on subjective opinion will always leave people upset one way or the other, but I think the other can be something fairly universally agreed upon.
My first problem, the subjective one, is that I personally found it offensive. I don't think serious, violent crime (rape, assault, murder, etc.) has much place being a punchline. But, like I said, this is totally subjective - everyone has a different threshold on what is 'offensive' and how far a boundary can be pushed before it goes too far. For me, it was too far. It was, at the very least, incredibly tasteless.
I think the more common problem, insofar as 'inappropriate content' goes, is that we are a community. For certain, seeing such images come up makes me feel on the outside of that community (which is, again subjective) - I think the objective bit comes in that we shouldn't, and I believe for the most part don't, want to present that kind of image to the outsider. We all want to enrich this community, right? We actively want more members, more contribution, more of that sense of camaraderie (although, I suppose, what kind of contribution you want to make and what kind of community you want this to be is a strong indicator of which side you'll take in this debate).
For the second reason, I think the mod was right to step in. I think I should make clear once again that "I'm offended" is not the same as "it's offensive" - however just because I was offended does not mean that the mod should or shouldn't have stepped in. They *should* have stepped in - because it's their responsibility to help enrich the community.
As a side note, the issue of free speech goes both ways - just as you have every right to post whatever you want, other people have the right to not listen. Although, I do think the mod should have contacted the poster directly and explained exactly why they were taking the action they did.