That is easy to do.
9-11. Im thinking you and I go and do the same in the name of God!! cool? no right?
Can we say with ease that GOD is not behind that sort of thing?
How about me and u set of a political climate that ends up starving a nation to poverty? Can we say that GOD is not backing that effort?
If we KNOW that a tradition like christmas is from a bunch of craziness and we know when we added it into christianity, then we can eliminate everyone that does that as well.
However, if this is a conversation that doesnt believe in god at all, we have to back up. So which are you? if you in fact believe in God, then we can start where I just brought up. but if you are an atheist, then thats something different.
I find that atheists are very very quick to assume that anything they find posted with a picture of George carlin next to it, or bill nye the science guy, or degrassey, is seen as "fact". yet they have never seen ANY of the studies they say they have done.