Also, as unbelievable as this sounds, some of the so-called "Third Temple" movements and organizations are involved in ecumenical and syncretic activities which are the absolute antithesis of what the Temple is all about.
In 1984, Yehuda Etzion was imprisoned for a plot to destroy the Dome of the Rock
I met Yehuda during my one and only trip to Israel! He met me at the airport and spent a couple days driving me around (where the ashes of the red heifer are burnt, Chevron, Shiloh, etc.). I wonder how he's doing these days.
IIRC, we had one of those on FR briefly; he offered to make freeper Salem the head of the Sanhedrin.