For instance, why give up your life for others? There is no justification for this in an atheist worldview, and without it, we would not have firefighters, police, or the military. Instead, we'd just have mercenaries that would just as soon massacre you instead of the enemy, if the enemy pays them more.
https://pitweb.pitzer.edu/academics/wp-content/uploads/sites...
Based on your reaction though with "red in tooth and nail[sic (claw)]" you seem more interested in your own preconceived biases than any good faith argument from science or otherwise.
Atheists still have to live in the real world. The real world doesn't run on people fearing god it runs on, among other things, laws and reputation. Most people wont steal from you because they don't want to go to jail not because god is watching. Most people don't screw over every person they meet because then they'll get a reputation as a person to not work with. Say you decide to play the long game and "pretend" to be good until you get your chance to betray everyone for your payday. Some might say that's just good old fashioned capitalist business, a system atheists and the god fearing alike participate in.
There are plenty of instances in our society where godlessness turns into immoral anarchy, such as the inner cities or the upper echelons of Wall Street.
On the other hand, even Islam, the most violent of the big religions, still teaches from the Koran that every person has something divine in them that gives them value. Islam has not conducted killings at the same scale as the atheistic regimes have.