"We encourage you to approach this moment with the seriousness it demands." 
Marrus apologized: "I am so sorry for what I said, in a poor effort at jocular humour."
That would seem the appropriately serious response.
Someone makes a small mistake and everyone jumps on him. The same for "environmental Barbie." Having a sense of humour means occasionally letting bad jokes pass. Fifty people were shot in Nevada yesterday. Lighten up.