From https://existentialcomics.com/comic/651
Mazdak was an ancient Iranian Philosopher, who believed the scriptures (Zoroastrianism scriptures, this was pre-Islam) dictated radical social equality. He thought all property should belong to everyone, and wealth shared equally. He was so convincing that he even convinced the king to go along with it, and was able to successfully implement many of his social reforms. He also believed in getting rid of clerics, because they held religious authority over the population, which he thought was illegitimate. Since they were the judges, he of course "lost", and was executed, along with thousands of his followers. As with most ages and societies, those with huge amounts of power and property have never been too keen on philosophers that want to take it away.
Eventually other rich and powerful Zoroastrian and Christian kings got wind of it, and challenged Mazdak to "debate" their clerics. These other kings were the judges, so naturally their guys won, and they brutally executed Mazdak and thousands of his followers. If Mazdak was a prototype for socialism, or even communism, I suppose you could say their reaction to it was a prototype for how to defeated socialism in the good old "marketplace of ideas".
(b.t.w., it may be out-of-topic, but it's everyday)
