According to the author, it seems that survival of the vittest is only something the evil humanists would do.
There is only a simple fact: Bad people do bad things, regardless of their religion, or lack thereof.
And the strong defeat the weak.
Not to mention that a lot of the time those bad people will gravitate toward some form of religion since it makes a handy weapon. It not only can supply a ready-made army of fanatics but also provides a compliant, exploitable population of followers willing to remain ignorant to anything their leader labels as off limits.