Couldn't agree more, honestly...but if atheists were honest with themselves, they'd admit that there is no way of knowing what kind of world we would have *If* religion was relegated to the dustbin if history.
As history shows, man as ALWAYS been religious/worshipping gods etc -- there isn't a time where this has not been the case. So its easy to take an idealistic "imagine a world without religion" outlook because we can make up whatever future we want with this viewpoint. At the same time, godless commies get widely ignored, or as in your case, downplayed because the US "did the same thing".
It's like a child imagining a world without parents (without the restriction of what the child can/cannot do) only to realize that its only an idea, fantasy, unreal dream that probably won't turn out the way they envision because we've never been without parents -- its easy to make stuff up in this case because we don't have a reality to scrutinize it with.