Why can they get away with ridiculing Mormons?

The musical “The Book of Mormon” is showing currently in Seattle.  Its entire run is sold-out.  It makes fun of Mormons.

Why can the producers get away with ridiculing Mormons? They wouldn’t be able to make a musical that ridiculed Jews or Muslims, or blacks or women.

Jews like Mel Brooks lampoon Jews. Gays make fun of gays. And blacks make fun of blacks. But outsiders generally can’t lampoon them.

Someone on facebook pointed out that ridiculing someone for their religion, which is something they freely choose, is better than ridiculing someone for their skin color or ethnicity.  But our laws and customs disallow discrimination on the basis of any of those factors.  We’re not supposed to make fun of peoples’ religious beliefs. Maybe that needs to change.

This person directed me to Twelve Beliefs the Mormon Church Might Not Want You to Know About;,  it lists some silly and empirically false things that Mormons (used to) believe.

But aren’t Judaism and Islam empirically false too?