The problem with Atheism is that, without a unifying philosophical force, one does not have a moral directive with which to do "the right thing."
This is half-right. Atheists do lack a religiously-based moral imperative against badness/wrongness/immorality/what-evil-synonyms-have-you.
However, that by no means implies a lack of any sort of imperative.
Societally speaking, crime leads to imprisonment.
In Humanitarian terms, commiting immoral actions leads to an increasing of suffering in the world, which is morally wrong because you are hurting others.
Speaking from a personal perspective, the golden rule comes into play. How would
you feel if someone victimized
you in an immoral act.
Sociologically, immorality is shunned by friends, neighbors, and other people. Loneliness is bad.
Even from a strictly practical viewpoint, the benefits of harming others more often than not fail to make such action worth it. And the cases where it is are why we have fear of the law.
Further, I hesitate to call fear-based religious imperatives a moral imperative.
Doing what is right from fear of the consequences is not making a moral decision, it is making a practical one. It is like the petty criminal who does what he does because he can "get away with it." Now, while it may be very hard (maybe impossible) to pull the wool over the eyes of the lord, any doubt about the existence of said lord (which, I would imagine, exists even for many Christians) weakens that imperative significantly.
Also:
Consider this. Who is more likely to commit murder? The man who fears the law, or the man who fears the law AND believes he will be rewarded for eternity in paradise for doing the Lord's work?
Now, this isn't a serious example. Not all religious people think like that; zealotry like that is a human flaw, not one that necessarily accompanies religion. But that fear of punishment in the afterlife? Same thing. Whether or not somebody worries about long-term consequences is a personal trait, not something that goes with religion. And what that example DOES show is that people will generally decide what they want to do, and if they're religious then they'll figure out how their religion justifies it.
Morality isn't fundamentally based on commands given by higher powers, any more than it is on fasting or burnt offerings. All forms of morality I've seen have boiled down to choosing an ideal and striving to meet with it. That ideal is often completely arbitrary; God, human happiness, social progress, whatever. I'm not saying that morality is completely subjective (choosing Hannibal Lecter as your ideal role model is not a Good Thing, for instance), I'm just saying that the process of working out moral directives works just fine without religion, and equally valid bases for moral behavior exist in the absence of religion.
What Bauglir said.