Is Satanism a religion? The courts have provided the institution with some protections. However, there are questions of whether or not it is really a viable religion.
First, a reminder from the unified model of religion: a religion must have a religioid belief ,and for any cultural element to be considered part of a religion, it must be integrated, in some way, either directory or indirectly, with a religiod belief. So the first question is whether or not Satanism has any religiod beliefs. Satanism does not have a belief in gods (including a form of Satan), afterlives, etc. So the usual suspects are out.
One potential option is the belief that there are no gods. While there may indeed be Satanists who believe that there are no gods, The Satanic Temple states that “the Satanist should actively work to hone critical thinking and exercise reasonable agnosticism in all things (The Satanic Temple).” If this is a fundamental part of the doctrine of Satanism, then it is antithetical to a belief that there are no gods, and indeed antithetical to religion itself, as agnosticism is inhibitory to the production of religioid beliefs: religioid beliefs appear to be ones that form when there is no empirical evidence to modulate them. Now, while the Satanic Temple only represents one form of Satanism, and there may be other forms that are religious, one of the more politically active institutions expresses itself in such a way that its form of Satanism fails to satisfy burden of proof necessary to label it a religion.
So if not a religion, what is Satanism? In many ways, Satanism seems to be a counter cultural phenomenon, specifically contrarian to Christian ideology. One of the key tenets of Satanism is bodily inviolability, which in many ways seems to be a direct attempt to protect against Christian doctrine on abortion and other related issues, and the desire to label Satanism as a religion seems to be a matter of wanting to be able to use the same types of arguments that Christians use to gain protections for the government.
This is problematic. While it is understandable that a group may want protections, the action of essentially stripping the concept of religion of all its inherent meaning, and simply calling any doctrine or philosophy a religion, in order to gain protections from the government, under the first amendment, delegitimizes the nature of religion itself.