Margaret Atwood claims atheism is a religion

[Metis]

Would you say that Theosophy, Buddhism, Shamanism and Wicca are not religions then? They all (some exceptions within Buddhism) have a very strong supernatural edge and yet have no concept of any deity/deities

I would say those are religions... I'm not too well versed on most of the above, but I can speak for Shamanism a bit.. at least shamanism in the sense of santeria... they do have a gods and saints that they pray to and perform rituals for.. I've been to one of the parties/celebrations for someone "becoming" a santera... they're assigned saints (i forget how) and they do things for them... wear certain colors, celebrate their saints birthdays, give offerings and pray to... i would call that a religion...

True, I was thinking more of Korean and Native American Shamanism there, Santeria does have deities of a sort but no supreme God-head which most modern day polytheistic religions do. Santeria is an indigenous/tribal religion but not really what we could call shamanistic in the sense of controlling spiritual forces like a magician devoid of any God figure.

I personally would describe any system, cultural or philosophical that can direct a human beings actions by directing it to refer to its precepts, thinking and way of viewing the world and not their own intuition a religion. This might sound not applicable to Athieism but Atheism does undoubtedly influence peoples actions; for one Atheists do tend to ascribe a far higher value to human life than say Muslims who relish the thought of martyrdom. Athiests generally also have a far stronger sense of  loyalty to kin than fanatical Catholics (as opposed to the mainstream 99% in the west), who are taught they must cast out unbelievers and heretics and their first loyalty is to the Roman Catholic Church, not their children or spouse.

There are a myriad of other examples such as rights ascribed to animals but as curious as it might sound, non belief in a sense would fit this definition of Religion. Because they don't believe Allah wants them to die in his name, they've far less motivation to blow up a bus full of people. Because they don't believe their God wants them to purge their lives of all sin, they're far less likely to kick their LGBT son or daughter out just on principle. In this sense the lack of belief is itself a world view, because there is nothing added to the equation when rationalizing ones environment aside from culture, the individual operates very differently from one who has inserted another modifier like Horus or El Cantare .

Of course there's many other definitions too, that's just the one I like to use because it incorporates almost every system I've encountered so far as well as focuses upon my research interests.