Tom, here's my take. LaVey grew up in a carnival. He was a carnie. As such, he had a highly dualistic view of humanity: there were the carnies, and there were the marks.
Carnies had their own lingo.
So LaVey starts the Church of Satan, and the way he goes about it is, he populates it with "carnies" (the people who were in on the joke but also saw the value in the serious parts) and the "marks" (the people who took absolutely everything seriously). One of the easiest ways to identify the marks was to ask them if Satanism was a religion. If they said yes, they were marks. Michael Aquino was a mark, despite being brilliant in certain areas.
Eventually LaVey realized that he had surrounded himself with too many marks for his liking. The stink nauseated him. So he started cleaning house. One of the marks who had to go was, of course, Michael Aquino.
Ultimately LaVey was able to keep the marks at arm's length. They paid their two hundred dollars and got their little red ID cards. They bought LaVey's books. They never, ever got invited to LaVey's home. Only the "carnies" were invited in.
Incidentally, the paradigm of an inner and outer circle is as old as the earliest secret societies. You find it in a lot of places. For example, many Gardnerian covens have inner and outer circles.
So no, Tom, Satanism is not a religion. It's a modern Hermetic practice whose participants are engaged in the Great Work from a dark, Left Hand, carnal, atheistic, misanthropic perspective. The goal of the Great Work (for the Satanist) is a more pleasing psyche.