Yeah have to agree. They usually do this as a stunt to get the religious clubs shut down when people complain. I have my reservations about religious clubs running on the school grounds but I don't really have a huge issue with them if they are voluntary not paid for with tax money and not restricted.

Now the people calling the satanists insane or arguing that they are a religion in bad faith, are absolutely right, but that's not a defendable legal position. You either allow any "religious group" to run their club, or you can allow no one. Personally I'm more on the side of let anyone do it so long as there aren't other legitamate objective issues with it.

In this case the best way to deal with the Satan club is to ignore it. They are basically well organized trolls and the best way to deal with trolls is to not give them attention.

Plus if the satanists are open about their activities then you can simply shun them IRL. They aren't going to be winning any school board positions with that platform so long as the school board is run right.