It’s a tradition on Christian holidays for memes containing crackpot history to show up. And also for the backlash to said which also often gets things wrong. No one knows what St. Patrick driving snakes out of Ireland is an allegory for, nor even if it really is an allegory or more of the kinds of folk tales that tend to be made about important people.
Take whatever I say with a grain of salt because I’m not a historian, but there are two main things that I think people in the US get wrong when talking about the religious history of Europe – firstly, we tend to think of early modern conflicts between Christian sects and extend that backwards, and secondly, there’s a lot of erasure of syncretism and coexistence of European or Middle-Eastern pagans and Christians.
It plays into fascist ideas to suggest that different kinds of people can’t interact without immediately wanting to genocide each other. There are plenty of cases of Christians coexisting with pagans or Jews or Muslims in European history and places where these interactions were common sometimes became broadly more tolerant – for example, Muslim Spain didn’t just treat Christians and Muslims as near-equals, it was also one of the better places to be gay in medieval Europe. It also plays into the idea that things always got better when we know that religious tolerance got worse at many points throughout European history. The reason that religious authorities had to get violent to get their way is because the people wouldn’t always adhere to their ideals of religious intolerance.
The memes act like Christianity “stole” this or that but the reality is, even if both religions did a thing, that’s not reason enough to know who did it first and it’s not theft if a pagan converts to Christianity but maintains some of their old rituals under a new garb. Nor for a new tradition to emerge among Christian-pagans and be continued by Christians. It’s not theft for me, an atheist from a Christian culture, to celebrate Easter or Christmas. Nor when a Japanese Mormon celebrates Obon, a Buddhist holiday. The only people who should take issue with these things are the kinds of people who think D&D is Satanic, and every reasonable person agrees that those people are ridiculous.