And the thousands of Muslim women and children who died in wars started by Christian leaders?
And, for that matter, you do realize that groups like ISIS target Muslims, too, right? ISIS are radical Sunnis so Shiite Muslims face as much persecution as Christians do.
And when was the last time you looked into the situation of the Bahais, who are growing here in North American but persecuted in much of the Islamic world?
How about the Muslims being attacked by Christians in Africa and by Buddhists in Myanmar/Burma?
Religious persecution goes on all over and it's not one tradition targetted nor is it one tradition doing it. We should be seeking to stop all of it, not seeking special protection for the group we favour. That just opens the door to more persecution.
Becoming one global religion might be a solution but I doubt it. Look at Christianity's history of sectarian violence. From the burning of "heretics" to wars between Protestants and Catholics, I don't see much evidence that being from the same religion actually helps. Ditto Islam, where minority sects are often targets of persecution.
Recognition that religion is a source of friction and beginning dialogue among the members (not just leaders) of various faiths to alleviate ignorance and fear is going to do more than pushing some kind of "religious union". We need think alike to love alike, as we UUs say.
Sure, it's utopian, but it is far more possible now than in the past simply because of the ease of communication and the development of multicultural societies like ours. My son thinks nothing of the fact that he is a secularized atheist hanging out with Bahais, Muslims, and Christians in his circle of friends at school. No persecution, no crusades, just teenagers with different points of view going to the prom together.
Maybe you should read this, "religious wars" account for less than 2% killed in warfare and that includes the Crusades. The word "religion" is a modern concept.
https://en.wikipedia.org/wiki/Religious_war