Christians were persecuted in ancient Rome. Like most angry atheists I've seen (and made) comparisons between Christianity and a cannibalistic human-sacrificing death cult... because that's technically what it is, no shade... but this presents an interesting explanation for why Christianity was so offensive to Romans and Greeks particularly.
The point seems to be that worship of a human, especially a ritually unclean human, violated a lot of local taboos and thus drew particular ire. So Christians would get blamed for bad fortune (but only once it arrived, due to the way the law worked).
This is the question I wrote my MA thesis on — and not only won the school’s prize for best thesis that year, but revolutionized Historians’ understanding of the persecutions.
In a nutshell,
1. the worship of a crucified Jewish miscreant (that’s how the Romans saw Jesus) as anything honorable, let alone as God-incarnate Himself,
2. the glorification of his crucifixion and the cross, indeed the glorification of ignominious failure, humiliation, and public disgrace,
3. the profession of faith in his physical resurrection and ascension,
4. the continued association with his flesh and blood (even if only symbolically), his spirit/ghost, and his name,
… all violated a host of the most horrific taboos of both Greek and Roman religion.
By their worship of “Christ and him crucified” Christians rendered themselves ultra-unclean, indeed absolutely detestable to the Greek and Roman high (good-luck) gods — the ones upon whose graces the well-being of the Greek and Roman cities and the empire were thought to depend. Consequently, “whenever the Tiber floods or the Nile doesn’t, up goes the cry, ‘The Christians to the lion!’”
Rome was not a modern state and its criminal justice system was accusatorial not prosecutorial. Charges could only be brought by the victims, and they had to prosecute the case themselves at their own expense. Likewise, Greeks and Romans alike knew that in religious as well as worldly terms, nothing was ever “absolutely clean” but merely “clean enough” or “not clean enough”. So in religious as well as secular offenses, the law was strictly re-active, not pro-active. The state waited for actual harm to be done before acting, when state punitive action was demanded. Thus, in normal or good times, though Christians were detested and regarded as suspect, the state would leave them alone.
However, in times of public calamity (natural disasters, famines, plagues, conflagrations, military debacles, and even economic depression) the Romans believed the root cause was that their high (good-luck) gods were displeased and had abandoned their sanctuaries and the communities in which they stood, leaving mortals to a mass influx of bad-luck gods bringing disease, defeat, disaster, dismay, and death along with them. And there was nothing that was so offensive to the high gods as paying divine honors to unworthy men and wallowing in death and its trappings (death relics, corpses and parts thereof, instruments of death, etc.).
In times of crisis or the wake thereof, the Romans and Greeks would look for the albatross-killers among them, and the diviners were quick to finger the Christians. Thus, Christians would be rounded up and brought before the magistrate and given a choice: cleanse themselves by abjuring the abominable thing — i.e., deny and curse Christ — or they would be judged nefas, whereupon the city would cleanse itself of them and their spiritual pollution by executing them ad bestias in the local circus. Tellingly, this only happened in towns and cities consecrated to the Greek or Roman gods, not in Syrian, Phoenician, Berber, Arab, Egyptian, or Celtic ones, because those gods and religions had different taboos, ones that weren’t violated by the worship of a crucified Jew.