Although the pyramid there looks like the Great Pyramid, it doesn't represent the Great Pyramid, but to the Bible Students it would represent the Christ Head and Body. The capstone at the top would represent Jesus as the Head, and the rest of the pyramid, the Church. The Bible Students at that time believed that those faithful who died would be immediately changed and be present and united with the rest of the resurrected Church. Hence "risen with Christ". The cross and crown - represents that the Church must endure suffering before they are glorified. Those who were faithful would have their names written in the book of life, as found in the Book of Revelation. The chapter on the Hidden Mystery in the Divine Plan of the Ages has an illustration of a pyramid, and an explanation of it. Also Chart of the Ages has pyramids, and there is a chapter explaining the meaning of the pyramid.
The Bible Students would never have thought of the Masons, this symbolism was well known by the Bible Students, who would have read the Divine Plan of the Ages. Russell taught that in the parable of the Wheat and the Tares, the bundling of the tares represents human organizations, including secret societies such as the Masons. Russell encouraged leaving all human organizations not only the churches of that time, but even unions if possible. Russell was extremely anti-organization, and the harvest of the wheat would have required the separation from the tares, and separating from organizations as much as possible. Russell's followers thought of themselves as the wheat, and being part of the Masons would have been frowned on and put in doubt their being of the wheat.
The Watchtower Society put the pyramid there and not dissident Bible Students. However, no matter how wrong Russell or the Bible Students might have been at that time, no matter how wrong how their interest in the Great Pyramid was, or the political motives that Rutherford might have had in putting it up, nevertheless they built it in honor of other human beings who had died or would die, and shows that they at least cared. It is unfortunate that those who are justly angry and hurt at religious abuse would let that override their sense of our common humanity. Mocking the dead and the bereaved is in poor taste as an argument of ridicule when despite our religious differences we will all die and lose people in death.