The point of posting the joke with Atheist changed to Muslim was to prove that some people think it's ok to insult certain groups of people and not others.

Hu Wan said he would not tell a bad joke where the punchline was unfounded and insulting about a religious group of people, but thought it was ok to tell a similar joke about non-religious group. Gypsy was trying to point out the double standards.

The joke didn't work since the punchline was not based on any acknowledged stereotype or fact. It was simply an insult.