A lot of people on the secular left seem to want to blame Anders Behring Breivik's massacre on Christianity, as he called himself a Christian and associated his massacre with rebuilding Christian Europe.
Now, some, such as Bill O'Reilly, have tried to deny Breivik's Christianity through the "No True Scotsman" fallacy, that is, the fact he killed so many people means he isn't a true Christian. Essnetially, "No True Scotsman" is a way of begging the question.
While that is a ridiculous argument to use, there is, however, a genuine question as to what Breivik's actual beliefs were. In his manifesto, at one point he says:
"If you have a personal relationship with Jesus Christ and God then you are a religious Christian. Myself and many more like me do not necessarily have a personal relationship with Jesus Christ and God. We do however believe in Christianity as a cultural, social, identity and moral platform. This makes us Christian."
In fact, he even refers to "Christian-agnostics" or "Christian-atheists."
Now, of course, some atheists are insisting that Breivik was a Christian, purely because he called himself one, and are defending their extremist nominalism by insisting that claiming that he wasn't is automatically the "no true Scotsman" fallacy.
Bollocks. Breivik is no Christian because he rejects Christian theology. Those who call him Christian simply because he identifies as one are engaging in extremist nominalism (that is, that words have no meaning other than denoting everything that is identified by that word - in other words, there is no definition of Christianity other than anyone who considers himself a Christian). I call this the "Idi Amin's a True Scotsman Fallacy," after Ugandan dictator Idi Amin, who referred to himself as the "last king of Scotland."
The "Idi Amin's a True Scotsman Fallacy" (i.e. the nominalist fallacy) is that by identifying with a group, you can be said to represent the group. For example, someone says that polygamy is an acceptable practice among Scotsman because the Last King of Scotland, Idi Amin, practiced polygamy. This is, of course, ridiculous, Idi Amin is neither from Scotland nor is there any evidence of significant Scottish blood as far as I know. His only claim to Scottishness is his decision to name himself the King of Scotland, which title, as far as I know, has not been recognized.
To deny that Idi Amin is a true Scotsman is not "no true Scotsman," it is maintaining a reasonable definition of Scotsman.
I should also point out that I doubt that most of those people arguing for Breivik's Christianity on nominalist groudns probably would not use the same argument if someone claimed allegiance to a group that they actually cared about. If Roissy called himself a feminist, or if David Duke called himself an anti-racist, I have a feeling that these people would pretty quickly start insisting on more formal definitions of these terms being used.
That is all.