Here's his point:
So atheism didn't tell the tyrants to go out and kill but it didn't stop them either did it? So much for moral grandstanding.
What tyrants he's talking about doesn't matter, there have been so many tyrants it is statistically sure that some of them were atheists (and we do know that some of them indeed were). This can also be enlarged to encompass murderers, thieves, rapists and any other kind of evil or inhuman behavior.
So it boils down to "atheism doesn't stop evil"
First let me state the obvious, this has no bearing on the truth value of atheism
So then, who ever claimed atheism would stop evil?
Actually since atheists don't believe in that all encompassing plan by god we pretty much acknowledgment the fact that evil (both human and natural) is a part of life.
What we do claim is that atheism stops religious evil, and the reason for that claim is obvious, no dogma, no enforcement of arbitrary rules from ancient books full of really hateful rules, ...
And (and this is important) atheism does not carry a historical dogma, it can be changed.
In re-reading this post my burdensome ability to "see the other side" was acting up again:
Some religionists will claim that the absolute basics of atheism (non belief in god(s)) in itself is or could be an attribute that is not beneficial to humanity so I'm not going to say that atheism can be changed anymore, the basics of atheism "non belief in god(s)" is unchangeable.
If atheism would carry a moral code and say how we should act it could be something like humanism to which I as an atheist subscribe. Its Humanist Manifesto is already on there 3rd edition so it is pretty obvious that humanism is not based on an unchangeable dogma like religion.
Anyway as it stands it has been sufficiently shown that it was not atheism that caused those particular tyrants to act so evil, in fact we can successfully argue that what gave those evil tyrants the possibility to act was more like religion.
And off course the claim is very easily reversed "religion doesn't stop evil" (plenty of historic and current events demonstrate this)
Here too, this has no bearing on the truth value of religion either.
update: I will sometimes just write what I think and then later see some possibilities of misunderstanding what I meant because of how I constructed the sentence plus I have a great (sometimes annoying) sense of "seeing the other side" so at first is seems so clear in my head and it still does but I can see how someone who did not grow up like me or did not have the same experiences as me would not see the logic of my point.