(CW: All forms of bigotry) The New Testament is also filled with nasty bigoted shit! Christianity is rotten to its core and is incompatible with a Marxist frame of thought

You could do this with literally any of the major monotheist religions of "the book" (Christianity, Islam, Judaism). It's extremely unhelpful as an argument to get people to leave religion because it does not address why religion exists, or why the vast majority of people globally are religious. To to that, you need to analyse the social function religion plays in our reality, of which organised religion is a key part.

Nevertheless, another reading can be made of Marx. The often cited phrase--"religion is the opium of the people"--is truncated. What follows this remark lets it be understood that human beings need opium, because they are metaphysical animals who cannot avoid asking themselves questions about the meaning of life. They give what answers they can, either adopting those offered by religion or inventing new ones, or else they avoid worrying about them.

In any case, religions are part of the picture of reality and even constitute an important dimension of it. It is, therefore, important to analyze their social function, and in our modern world their articulation with what currently constitutes modernity: capitalism, democracy,
and secularism.

We also need to move past the false dichotomy of religion and secularism being incompatible as concepts, in particular with regards to Christianity in the western centric parts of the world. The reason non belief, in agnosticism or atheism, grew so much over the past few decades in the West was because the church held onto some archaic positions about the world being 6000 years old, evolution being false, and homosexuality being morally wrong. Religion had detached itself from factual reality, it was easy to bludgeon in this regard. But that is no longer the church or society we are in now, by and large (there still are of course many extreme reactionaries). Modern secuarlism has essentially freed Christianity from its shackles here, there's no need for modern Christians to believe in such archaic nonsense. For example, the Catholic church accepts evolution as a scientific theory, and no longer considers homosexuality inherently sinful. This form of "secularism combined with religion" may in fact lead to reinforcing belief in the long run, and even leading to an increase in Christianity over the coming years in the West. Trying to foster an increase in non belief in this environment is very different to that of 10, 20, or 30 years ago. When I became an atheist, it was in that old environment.

Contrary to a widespread Eurocentric preconception, however, secularism is not peculiar to Christian society, which demanded its liberation from the heavy yoke of the church. Nor is it the result of the conflict between the "national" state and a church with a universal vocation. For during the Reformation, the church is in fact "national" in its various forms--Anglican, Lutheran, and so forth. Nevertheless, the new fusion of church and state does not produce a new theocracy, but rather, one might say, a religious secularism. Secularism, even though the reactionary ecclesiastical forces fought it, did not root out belief. It even, perhaps, reinforced it in the long run, by freeing it of its formalist and mythological straightjackets. Christians of our time, whether or not they are intellectuals, have no problem accepting that humankind descended from apes and not from Adam and Eve.