I look at establishment of church activity in the public school as an encroachment and foot hold. Even if it takes place off school property, if it reduces student time in the school building, simply moved to another location, but within the established curricular day, then it is curricular. This is a fancy dance to circumvent the law and separation of church and state. Identification of "public school" students, and letters sent to public school superintendents makes it an obvious target. The fact they go so far to simultaneously appear to distance themselves makes the program suspicious.
Some Christians believe most non to seldom practicing people too stupid, and too liberal to think and reason for ourselves. We don't know any better. THEY know the truth, and they're convinced our lives will be better if lived under THEIR truth... uh...er...belief. They're doing this for our own good.
Establishment of their classes in a public school is one step toward saving our children from us. Just like with abortion, they attempt to speak for the children who in their estimation have no voice.
There is no means of rational argument with them because they're convinced. Their belief is their truth, even when you can prove otherwise. Belief is what many people generally accept to be true, but can't be proven. Unfortunately they don't understand the criteria necessary for proof.
It is the same as "God told me to tell you..."
No, if God wants to tell me, He tells me. He never tells somebody else to tell me. Nobody is His secretary, and if He did, and they were, He would be no God I would have a relationship with.
A pastor for whom I have great respect, once gave a sermon, which began as a biology lesson. People in the congregation fidgeted and were increasingly uncomfortable. Then, just before the conclusion, he dropt the other shoe. "Creation" should not be taught in biology class either.