From reading the above comments, it appears that, not terribly surprisingly, the pope's comments have been read without a full understanding of the complete matter at hand. In particular for those of us in the West (i.e. Europe and North America, from where I assume most everyone commenting lives), we have all been influenced by Christian thought. As a result, most atheists as it were are rather "Christian-flavored" atheists (whether they believe it or not) and they tend to, for the most part (with a few notable and pretty much the same exceptions), agree with Christian moral teaching, like, for instance, that all human life is valuable (thus our focus on charity through personal or governmental means) and that murder, rape, theft, etc. are wrong. However, given that atheism is "devoid of content" as DaveH pointed out, that void can be filled by a lot of different things. In the West, it is usually filled, as I explained above, by a Christian-flavored world/moral view because that is the still somewhat dominant culture. However, it is not necessary that this be what fills the void. Rather, what fills the void can be something that looks a lot more like Nazism, or Lenin/Stalin style communism, or pretty much anything else.
What the pope is trying to say, then, is that atheism (given its lack of any firm moral grounding) has a strong potential, in some cases, to lead to these problems because it is an empty cup that can be filled by either good or evil, and sometimes it gets filled by evil. It is then, only by accepting Christ and living as He (Christ) teaches, that we can achieve salvation (the more "religious" component of Catholicism) but also create a better world (i.e. through charity, being good, etc.).