The entire point of the Satanic Temple is to demonstrate that if government buildings and operations are to represent one religion (namely Christianity) they must also allow other religions. “Even as we prefer public policies respecting secularism, we feel that opportunities — such as this — to establish an equal voice for contrasting religious opinions in the public square, tend to favor marginalized, lesser-known, and alternative religions,” The Satanism being preached is essentially philosophical, and their canon is Anatole France’s Revolt of the Angels, taken completely allegorically.
The point of all of this is to diminish the intrusion of religion into the state.
"The Satanic Temple was actually conceived of independent from me by a friend and one of his colleagues. They envisioned it more as a “poison pill” in the Church/State debate. The idea was that Satanists, asserting their rights and privileges where religious agendas have been successful in imposing themselves upon public affairs, could serve as a poignant reminder that such privileges are for everybody, and can be used to serve an agenda beyond the current narrow understanding of what “the” religious agenda is. So at the inception, the political message was primary, though it was understood that there are, in fact, self-identified Satanists who live productive lives within the boundaries of the law, and that they do deserve just as much consideration as any other religious group."
https://www.vice.com/read/unmasking-lucien-greaves-aka-doug-mesner-leader-of-the-satanic-temple