As a Jewish atheist who resents Christian privilege in America and as one who finds Christian teachings ridiculous, I'm not especially fond of that religion. But if we're going to criticize it, let's do so objectively.
The regressive Left, which reflexively defends Islam no matter how often Muslim extremists commit violence against others, wasted no time in pouncing on Robert Dear who attacked the Planned Parenthood center, as an example of Christians who also commit terrorism ("See? They do it too"). And some leftists are even calling Dear a "White Christian terrorist"
The difference is that Muslims who terrorize others as in the recent assault on Paris openly acknowledge that they are doing so in support of Islam. So far Dear has not justified his actions in the name of any religion or race. Instead he simply said "No more baby parts". Non-religious motivation was also definitely true for example, of the Oklahoma City bomber, Extreme Timothy McVeigh, a right-wing extremist. His reason was hatred of the U.S. federal government. In short these two were not using Christianity as an excuse for committing their heinous crimes. That's why it's inaccurate to label them as Christian terrorists.
To put it another way, don't we atheists object to the cliche that we often hear that "Stalin and Pol Pot were atheists, and look at the atrocities they committed."? Our response is yes they were evil men who did terrible things, but they did not carry them out in the name of atheism. Likewise, that is the same standard that we should apply to Christians and members of other religions whom we condemn as terrorists for their heinous acts: Did or did they not do so so in the name of these beliefs? If not then let's not use religion as a target if there's no basis to do so.