Christianity is just one of many Eastern Mystery Cults that made their way to Rome. The one thing that differentiated Christianity is, like Judaism, it was intolerant of other religions. You could, for example, belong to the cult of Isis or Mithras and still offer sacrifices to the Roman Gods. Christians and Jews both refused to do this, or to pledge allegiance to the Emperor. That is why they were persecuted.
Romans threw Christians to the lions and lit them on fire to light the streets of Rome because Christians don't sacrifice to the Roman gods, and you conclude that it was Christians who were intolerant. You've shut yourself off even from ordinary reason.