As religious faith has declined, ideological intensity has risen

Hard to answer without first defining evil (ideally avoiding Godwin's law).

He goes in very great details (although this is hard to read even for me as a native French speaker) about how his intellectual contemporaries (most of them Marxists) used to believe in the same kind of myths that are usually associated with religion. The proletariat as a messiah, the Left being the road towards Progress and the inevitable fate of Humanity pass to the next stage, that in all societies History is unavoidably leaning towards the same finality, the State has replaced Providence and is seen as a guide that shepherds the people.

I see a lot of talk in this thread about making the definition of "religion" meaningless by broadening it too much, but I think the definition that gets narrowed in is "the phenomenon of humans engaging in dogmatic belief." A good example of this is transhumanism, specifically, the idea that you can upload your mind to a computer. It is all but given based on our current scientific understanding that the mind is inseparable from the body, yet somehow particularly atheist people behave as if they are separate things. This is a dogmatic belief.

Other closely related behaviors are ideological movements. I believe that religion is largely social in nature and driven more by social pressure and community/family and less by actual rational analysis or any other method of coming to conclusions about the world. I think it shows in the decline of traditional religion and also in the rise of what are often being termed "religions" these days by detractors (correctly in many cases, for example the Gaia worship end of times cult). When that is taken into account, the irrational behavior of swathes of people who hold as a core identity characteristic their perceived strict adherence to rationality makes a lot of sense.

I know I have a religion, I don't know what it is exactly, but I'm a human so I have one. But I try to be open to any idea I hold being challenged, I'd like my belief system to be as close to the truth as I can get it, and that means ignoring social proof and being prepared to find out that anything and everything I believe is wrong. Of course, until I find out I'm wrong, I think I'm right.

It’s a huge book but the basic takeaway is this: the modern secular world is a thing that was created over the course of many centuries and cultural developments. It is not merely the subtraction of so-called primitive beliefs. The “subtraction thesis” is the predominant model of how most people (and until recently, religious scholars) interpreted the secularizarion process.

This means that the same basic historical and psychological forces are at play, but they’ve just been morphed and combined in different ways. What is truly new about the modern secular world is its immanence, which basically just means it is not concerned with a “world beyond” this one, and its “cross pressures”, or the state of being aware of other viable alternatives to one’s belief system.

https://en.m.wikipedia.org/wiki/A_Secular_Age

One problem I see with this line of thinking is that it's often faux intellectualism, in the sense of not even attempting to define what a deity is in the first place, instead taking the lazy approach of "whatever you think god is doesn't exist". What exactly is a deity in the first place anyways? Bearded guy in the clouds? A lot of christians don't believe in that either. Jesus (i.e. a human)? A certain north korean leader that had similar godlike fame among followers most definitely existed (godhood claims notwithstanding). The holy spirit? Read "spirit" as you read "spirit of the law". Some flavors of pantheism actually argue that the concept of "an omnipotent omnipresent entity that nevertheless grants us free will" can be perfectly explained if said entity is the laws of physics.

As we can see, there's a pretty big spectrum ranging anywhere from strawmen to things that do exist. IMHO, proper atheism needs to be able to argue against the entire body of theism, not just narrow set of christian beliefs, and as such it's a belief system that doesn't fit many people. There's agnosticism (basically, "I don't know if god exists because the evidence doesn't convince me"), which is a much easier belief system to actually defend, and which I think describes more accurately the belief system that a lot of self-proclaimed atheists actually subscribe to.