It seems to me that the line between the “privately told” incredibly insensitive joke and the “publicly broadcast” incredibly insensitive joke is that, in the former, the person telling the joke has at least a reasonable chance of ascertaining whether there is anyone in the room who will be personally hurt by the joke.
I live on Long Island and work in a court building where there are many people with varying degrees of connection to both the dead and the survivors of the WTC. I haven’t heard a single joke on the subject of 9/11 – and I assure you that my friends and coworkers are a boisterous group.