It is really no sillier than everyone suddenly remembering that they brought food and starting to share with their neighbors, The whole purpose of these theories was to remove anything even remotely miraculous from scripture and to de deify Christ. Then they could push their concept of what Christ really was. A good man, a moral man with unique views on the world and life, full of love and compassion for his fellow men and women…
To the developers of liberal Christianity, there was nothing miraculous in the Bible, everything could be explained logically, irregardless as to how tortured their reasoning had to be to accomplish it.
Their reasoning was that traditional Christianity had been so compromised by new knowledge and scientific developments that only radical surgery could save it. So they took everything that was miraculous and lopped it off, creating the social gospel.
Before you brush this off consider this. Liberal Christianity developed in the mid to late 1800’s in the Protestant communities and so infected protestantism that there was actually a backlash against it that created the entire fundamentalist movement within protestant circles thats exists today. . Even today, if you speak to many protestant pastors, you will find they don’t believe in the Trinity, the Virgin Birth, the Divinity of Christ, Heaven, Hell. miracles etc. The fundamentalists do, but the mainstream communities do not to a great degree,
Also consider that many of the ideas that I have mentioned started creeping into Catholicism, albeit at a much slower rate at about the same time. It was only later in Catholicism, in the period between the thirties and the seventies when these ideas started to take hold with increased cooperation and interaction between Catholic and Protestant theologians and seminary professors,.