Why would someone lose faith in Christianity in mid-Victorian Britain? What were the most persuasive reasons for believing in the Christian religion?

At the beginning of the Victorian period, science was generally in accord with religion, and the study of nature was conducted in such a way that new discoveries were seen as evidence of God's design. Science and theology were not viewed as separate disciplines; it was easy to continue to believe in God, as the country had done for centuries, when influential theologian-scientists like William Paley argued that the beauty of nature supported, rather than contradicted, what was written in the Bible. Faith was almost universal; people did not generally need a compelling reason to believe in God, as they had not been presented with compelling reasons not to. Christian faith was the norm, and anything else represented a divergence.
This began to change in the mid-Victorian period during something referred to as the Victorian Crisis of Faith. This coincided with new scientific developments in geology and anthropology which challenged the long-held belief that Genesis could be interpreted almost literally. From the 1840s, it became evident that the earth could not be argued to be only a few thousand years old; geological discoveries contradicted this utterly. This was the beginning of some theological arguments for the nonliteral interpretation of the Bible. Meanwhile, Darwin's Origin of Species raised the specter of evolution, something which at first outraged and then perplexed the community, as it suggested that God might not be the divine Creator after all. Political and social upheaval across the continent, inspired by the French Revolution, suggested that the status quo could be subverted by the people: although people in Victorian Britain no longer literally believed in the divine right of kings, the Queen and the Church were intertwined politically and religiously. The idea that the monarchy could be overturned raised the idea that religion, too, could be done away with.
By the end of the Victorian era, then, religious faith was no longer the unshakeable thing it had been in 1837. Even for those who were still Christians, there was far more divergence in the types of faith that were practiced: not everybody was an Anglican, and new sects, including Spiritualism, developed as an alternative means of explaining how science and religion could work together.
http://www.victorianweb.org/victorian/science/science&religion.html