Because to the extent that Muslims can be considered to be heretics of Arian Christianity (see above), this conflict can be looked at as a civil war between the People of the Book. As our Confederate friends can assure us, a civil war is much more bitter than a war between strangers.
However, many centuries later, this does not "excuse" the re-emergence of such behavior. I know the current persecution didn't begin overnight. "Re-Emergence" may not be the best choice of words. It has been increasing as the Christians increase in number and expand into Muslim-dominated terrtories.
But as most of us have gotten over the Civil War of the US in that northerners and southerners can co-mingle somewhat peacefully 150 years later, the civil war between the Arian Christians and the Muslims should have died out a very long time ago.
I do realize that battles fought on religious premises do not just suddenly die out, however. I guess it's just wishful thinking that the "My God is better than your God" syndrome would just go away.
Thank-you for your thoughtful and informative response.