The Sect of The Apocalypse aka the Apocalypsites and the Knights of the Apocalypse.

The Sect of The Apocalypse aka the Apocalypsites and the Knights of the Apocalypse. 

Image from The Warriors Of The Wasteland/The New Barbarians circa 1983 and 1984 

 A religion whose followers believe that their ancient scriptures foretold the destruction of galactic civilization, some even believe their church's divine duty is to end the sinful civilizations of the galaxy. They believe no more children of the races responsible for the War of Extinction or the Period of Shame should be born. They believe it is the divine will that civilization collapsed and all races involved should die out as divine vengeance and judgement for civilizations' sins. Most followers of this faith are peaceful, they avoid propagating their species through various means, pray for divine salvation, preach zero population growth and spreading their take on God's plan as they see it. Generally this group supports suicide booths and legalization of suicide by any means, population controls through forced sterilization, capitol punishment of all kinds, and anything that will legally limit or decrease the sinful population. 

However a secret society exits within the larger faith known as the Knights of the Apocalypse, this group actively works to sabotage the rebuilding of planetary civilization and galactic civilization, any activity that will prevent "the seed of the bringers of the apocalypse" from spreading, or hinder it is considered a good thing... naturally the Knights do not want to die themselves as they have work to do, but they often propagate their faith on planets still on the edge of barbarism and not ready to go back to the stars, they encouraging their followers to do God's work by mass murdering any "breeders"... and recruiting those young enough to train to be the next generation of Knights. These Knights are really twisted murderous cunning psychopaths. The Knights will however generally avoid killing communities of the converted Apocalypsites probably because they can recruit new Knights from them and receive aid as needed in support of their glorious work. The Knights have also been known to protect the Apocalypsites as long as the Knights feel they are spreading the word and participating in the divine plan of extinction. The Knights have been known to kill usually without mercy and using torture any Apocalypsite settlement or community they feel is tolerating heresy for example allowing children to be born amongst them. Kidnapping or adoption of children to convert them is not considered heresy by either group, neither is killing .children considered immoral. Apocalypsite communities in civilized space promote peaceful extinction as atonement for the sins of the ancestors and always claim to follow the local laws.

Image from The Warriors Of The Wasteland/The New Barbarians  citca 1983 and 1984

How closely the two groups are connected is not really known though, but it is suspected that the upper hierarchy of the Apocalypsites actually promotes both approaches towards the end of all life and controls the Knights. 

The Knights symbol is based on an ancient Terran symbol called the Ace of Spades. 

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(This Sect was inspired by ideas in Gamma World and very bad after the nuclear holocaust movie The New Barbarians/The Warriors Of The Wasteland, and the events in Star Empires timeline.)