The argument used by Alexander Hislop to explain Rev 17 as a mystery religion, is that every false religion in the world is the worship of a woman named Semiramis and her child, Tammuz, the reincarnation of Nimrod. His argument is that a mother-child religion spread through the entire world after the fall of Babel, and is now the predominant religious system in the Catholic church. This religious system replicates the worship of Semiramis and Nimrod in the form of a mother goddess and child god named Tammuz. He claims that Mary is the mother goddess, and Christ Jesus is Nimrod in his reincarnated state as Tammuz. Mary and Jesus are the same beings as Semiramis and Tammuz, but the names are different since the languages had changed.
His argument is that Mary and Jesus are imitations of Semiramis and Tammuz reintroduced into religion, and the birth of Christ Jesus, was a replacement for this ancient Babylonian mystery religion. He ignores any reference to the rise of fertility cults consisting of a variety of deities that dominated the Mesopotamia.
History shows that the Mesopotamia was filled with a mixed combination of occult rituals, idol worshipers and a saturation of fertility deities post-flood. History has no mention of a woman named Semiramis until the 8th century BC, long after the tower of Babel fell and, Nimrod no longer walked the earth. And, her name wasn't Semiramis, it was Queen Shammuramat. But her memory was expounded upon, and included in the writings of many Greek historians, beginning with Greek physician and historian, Ctesias (5-4th C BC) who connected her to a mythological character, King Ninus.
According to Greek mythology, King Ninus ruled Assyria in 3000 BC. These myths and legends are what Alexander Hislop based his research on, and are now taught in the church as actual Biblical or, historical occurrences.