ATHEISM
I have a friend who was a member of the church as a child. He then studied the various versions (translations) of the (one and only) Bible, the Koran and much of Eastern religions, and he even went all the way to learn old Hebrew to study the Talmud in depth. Somewhere along the line he left the church. Today, he neither goes to church, nor takes part in religious ceremonies, nor belives in God or any other deities. Yet he'd feel offended if anyone called him an atheist. I'm sure he could explain, so next time I meet him, I'll ask him -- that is, if I remember and can be bothered then. To be honest, as of today in our Western religiously tolerant societies, the "theist versus atheist" dichotomy (which comes from the Age of Enlightenment, so just another yesteryear's story) is an academic distinction of rather little practical value.
Personally, I'm third generation without religion. And I wouldn't even know what it means(feels like) to be religiously active or atheist. Sometimes, however, I wish I'd understand the religious sentiment a little better (William James' "Varieties of Religious Experience" was an interesting read). But generally, it just escapes me. However, I do acknowledge religious feelings and consider them legitimate/genuine. JR has given some very good examples. I not only tolerate people's religious feelings, I respect them -- cos I (generally) respect people.
Example: If there was a religious sect that claimed their God's (or their gods') will was that they run around naked in public all day, I'd say: "Be my guest, but don't start funny rubbing games. Don't expect me to follow your example and don't complain if restaurant owners deny you access." For myself, without voicing it, I'd think: "Is that really comfortable in winter?"
As for me, anyone is free to believe what they want to believe, and everybody should be free to do what they want to do -- as long as they don't molest other people with it (especially me) and cross civil code lines.
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BACK TO THE ATTACKS
Seriously, I am a bit surprised that the attacks in Paris have triggered a discussion of religion(s) here. While critical self-reflection is never harmful (for mental health reasons), I don't understand what religion has to do with this. Aint't that partially buying into the "clash of cultures" discourse?
The last thing I want to see is politicians or anyone else saying: We are going to do this and/or that -- and may the force (God) be with us. No, please!
A line has been crossed and it calls for a response. The French have started cleaning up at home, which I think is more than due. But honestly, I'm more concerned about the pending strengthening of the extreme right wing than any religious motivation that those attackers might have had (and I seriously doubt they had any).