Most theists refuse to understand that they are controlled by their belief system. Everything in their brain is filtered through that belief system. Some can, but refuse to examine the validity of the belief system. And the few that do examine it rarely hold onto it. The west has been under the boot of Christianity for 1700 ish years. It isn't true. But let's look at the Hebrew bible instead of arguing about Jesus. The penteuch/Torah/Septuagint was fabricated in 273ish BCE. Noah, Moses, Abraham, the tribes of Israel, etc...all fictional. Evidence in the Jewish section:
https://en.m.wikipedia.org/wiki/Elephantine_papyri_and_ostracaThere is excellent evidence how they made up their holy book and why. Russell Gmirkin is probably the best source on this. He has written multiple books and done dozens of interviews if you can't afford the books.
So the foundations of Judaism, Christianity, and Islam are a jewish lie. Don't worry, Buddha and the other founder gods/holymen were fictions, too.
Why so much ferocity? After millennia of being under the boot of idiots who would chop your head off, burn you alive or hang you for not believing in their magical sky daddy we finally have the chance to be free of childish nonsense. The internet has given people a chance to put the evidence and facts out there. The church was the monopoly media for millenia. This is a chance to be free.