Religious liberty/freedom has legal meaning that is derived from the Constitution.  You can't apply those words outside of that important context.  Plain and simple, under the Constitution, religious freedom means that the government can't make a law that forces you to participate in a religion nor stop you from participating in your chosen religion.

If you don't want to serve a Satanist, don't serve a Satanist.  If putting the Devil on a cake for, say, a Satanic ceremony goes against your religious beliefs, do you really think that the government should force you to?