hanged*
The problem is that these people don't know the difference between "promoting, advancing, aiding, facilitating, endorsing, or causing religious prayers or devotionals during school-sponsored events" and privately praying to themselves during said school-sponsored events.
Essentially, their religion mandates cult-like indoctrination and evangelizing, which makes their religion incompatible with other people's rights, freedoms, and choices. Yes, I am implying that such religions as Christianity and Islam are inherently incompatible with living in a free society.