Too easy:
"Vicious, murderous, genocidal" people or organizations are acting outside all of the principles of Christianity, and are acting completely against the example of the founder of the religion, so their claim to be "Christian" is a lie. That simple. Fred Phelps is obviously not a Christian, as he violates every tenet of Christian philosophy.
"Vicious, murderous, genocidal" people engaged in jihad or child abuse are completely in compliance with the basic philosophy of Islam, and are following the example of Mohammed, and so are still Muslim.
Too easy:
The "vicious, murderous, genocidal" people and organizations were often acting with the complicity, sometimes with the express approval, and occasionally at the direct orders of the leaders of Christianity.
The only difference between a fatwa and the Doctrine of Discovery is that Muslims following those fatwas haven't succeeded yet.
Further, the Bible contains many, many acts, directly ordered, or even committed, by God that would make any civilised person vomit. As does the Qu'ran, which also contains admonitions to Muslims to practice love, honour, and charity.
I've read both documents. Have you?
Not that it matters. As it says in the Bible "by their fruits ye shall know them." Matthew 7:20.
I personally experienced the fruits of Christians many places, most particularly at Chilocco Indian School in Oklahoma.
You may have some abstract grievance with Muslims, but I'll bet no Muslim has ever done you direct harm in the name of Islam. I, on the other hand, have experienced substantial direct harm from Christians who were acting in the name of Christianity (specifically, they were "beating the Devil out" of me). Frequently misquoting Proverbs 23:13 and Hebrews 12:6-7 whilst doing so. Just as Christians throughout the ages have quoted the Bible to justify their insane viciousness in everything from holy wars to massive child abuse to genocide to murdering doctors.
So pardon me for not thinking much of Christianity.
The good news is that, despite my track record with Christians, I take each as I find him. Some are wonderful people, most are pretty ordinary. Some are horrible. Much like the Muslims I have known.
You might want to consider looking at Muslims the same way. Just a thought.