In Darwin's own words his beliefs fluctuated considerably. The general trend was from Anglican Christianity to agnosticism. But, there is evidence that he was a believer at some points in his life, even though agnosticism grew quickly. Hence, I don't think it's accurate to say that he was never a Christian.
What his personal beliefs were I can't tell you, but I've never seen the slightest indication of a profession of faith. He describes being late to school one morning and prayed as he rushed to school. He said he was sure if it was the praying or the hurrying that helped his progress. He calls the doctrine of hell a, (expletive deleted), doctrine that would condemn his dad and bother to everlasting torment because they were both atheists. Today we look at a view like that and think, yea so what, but in that time it came as a shock to the church people in that day and age. This might sound a bit harsh but I simply see it as an expression of a naturalists worldview, a systemic pattern in his thought and work.
As above, there is evidence including Darwin's own words that he was not always agnostic and that he was a believer at some points in his life.
All I can tell you about that is he attended an Anglican church and accepted what he was being taught about special creation. This is a guy who knew so much about how favorable traits were passed on to the next generation that he married his cousin. One of the first things to be compromised is the immune system and he lost his daughter Anne to scarlet fever. In the wake of this terrible loss he published On the Origin of Species. Right up until his first book hit the presses he was in correspondence with the philosopher Asa Grey, who he mentions in the opening line of On the Origin of Species. Another philosophy was profoundly influenced and encouraged by Darwin's book, Karl Marx:
“Darwin has interested us in the history of Nature’s Technology, i.e., in the formation of the organs of plants and animals, which organs serve as instruments of production for sustaining life. Does not the history of the productive organs of man, of organs that are the material basis of all social organization, deserve equal attention?” (Das Kapital. Marx)
A little known fact, did you know the Scopes monkey trial had very little to do with evolution? The biggest issue was social Darwinism. Notice Marx emphasizes history and the 'material' basis for life and social organization. Now Darwin, some will tell you, was being encourage by Marx through correspondence to speak to the issues of religion which Darwin said he had always avoided. At the end of On the Origin of Species he even says he was certain his book should have no effect on the readers religious views.
My sole interest isn't to try to expose the inner recesses of Darwin's private beliefs but the effect of his philosophy of natural history on western academic and scientific thought. Darwinism, while being benign in many ways, is clearly a materialistic worldview that excludes God as cause categorically as a central premise. It's not a good thing or a bad thing, but it's evident, obvious and frankly an unavoidable core tenant.
Yes, the general concept of survival of the fittest and evolution can be applied to other domains. (E.g. genetic algorithms, evolutionary views of business marketplaces, etc.) Darwinism applied to other domains does not always work, in my opinion. E.g. I'm not sure that in businesses do survive or not based around survival of the fittest trends as clearly as living things.
The concept of survival of the fittest seems like a reaction to an ongoing population explosion that they were experiencing in the mid-nineteenth century. Based on the observations of Malthus there was something they would call the 'geomentric growth of populations', and the ensuing struggle for existence. It is also thought to be a leading influence on the reasoning of Oliver Wendel Holmes and his famous majority opinion on the issue of Eugenics:
Buck v. Bell, 274 U.S. 200 (1927), is a decision of the United States Supreme Court, written by Justice Oliver Wendell Holmes, Jr., in which the Court ruled that a state statute permitting compulsory sterilization of the unfit, including the intellectually disabled, "for the protection and health of the state"
A decision by the way, that was never overturned by the Supreme Court.
I accept that these are your conclusions. But, I've also looked into these things and revised them now to check, and I don't agree on Darwin never having been a Christian.
I don't know and I'm not sure it's all that important. All I know is he quietly acknowledge certain thing religiously but I've yet to see a profession of faith. What interests me is his influence on science, politics and legal theory. Whatever it was in his heart and mind it has become a catalyst for dialectical materialism and has exercised a deep and lasting influence.