Well, if one is able to mind read, and know exactly why somebody is celebrating something, then yes, they would be sinners.
Why this underlines my point--already forgotten from the beginning of the thread--is that one of Maher's original points was that many people are celebrating bin Laden's death from a perspective of vengeance; which, if one is a Christian, is distinctly going against the message of their Messiah.
Anyways, the Church also recognizes the concept of a just war. So once again we're back to contradictions. It's nothing new. Other than to Maher and Hardner.