The group doesn't seem to represent "Satanism" except in a very small way.
I don't think anyone claimed otherwise.
I don't have a way to tell how true the group's beliefs are, and how much might be a cover for usually frowned upon activities.
Pardon me for making an example of something:
You don't have a way to tell how true a Christian's beliefs are, or whether their involvement is a cover for, say, their homophobia - "It isn't me! God said it was wrong!"
Replace the referent there from Satanic Temple to Christian, it becomes offensive, doesn't it? Then maybe the problem isn't with the referent, but with the prejudicial nature of the question.
And you are correct, this is exactly why government needs to stay out of, and protect, religious practices. Because our fellow humans cannot yet be trusted to do so.