Its not just French cartoonists that religious extremists kill. The Taliban, and like minded organizations, frequently save the worst violence for people that, in the view of the West, are their own. Imagine if the handful of murderers in Paris had killed 150 children. But that is what they did in Pakistan, on December 16, 2014. Where was the global outcry then?
On New Years even a suicide bomber in Yemen killed 33 at a celebration of the Prophet's Birthday just because they were, essentially, a different denomination.
You really don't have to look to far to find equally horrific crimes committed in the name of Christ.
Larry McQuilliams had a copy of “Vigilantes of Christendom " when he shot up the Mexican Consulate in Austin. That document is produced by the Phineas Brotherhood, a radical Christian White Supremacist group. But wait, you cry, why do you have to call them "Christian"? Because that is what they claim to be, just like the murderers in Paris claimed to be Muslim. They may believe it. Doesn't make it so.
The 1996 Olympic bombing in Atlanta? Army of God. The bombing and slaughter of 77 in Norway in 2011? A self proclaimed Christian Crusader. The whole "Kony" thing that was all the rage for a while due to the use of child soldiers in Uganda? The Lord's Resistance Army.
Need I mention the KKK, the IRA? We could go further back. Timothy McVeigh and Guy Fawkes?
Sure, you might say that what they teach and practice isn't Christianity; but that is the point. What the radical Islamists teach and and do isn't Islam. They do what they do because they want to do it, for their own reasons that they might have justified with faith. Doesn't mean they represent the faith.
Killers be Killers. Nothing else.